diff --git a/src/AppRouter.tsx b/src/AppRouter.tsx
index aa66b59f..382e6a31 100644
--- a/src/AppRouter.tsx
+++ b/src/AppRouter.tsx
@@ -28,6 +28,7 @@ import { WebxdcFeedPage } from "./pages/WebxdcFeedPage";
 import { TreasuresPage } from "./pages/TreasuresPage";
 import { ThemesPage } from "./pages/ThemesPage";
 import { ThemeBuilderPage } from "./pages/ThemeBuilderPage";
+import { ExternalContentPage } from "./pages/ExternalContentPage";
 
 /** Redirects /profile to the user's canonical profile URL (nip05 or npub). */
 function ProfileRedirect() {
@@ -71,6 +72,7 @@ export function AppRouter() {
           <Route path="/decks" element={<KindFeedPage kind={37381} title="Magic Decks" icon={<CardsIcon className="size-5" />} />} />
           <Route path="/themes" element={<ThemesPage />} />
           <Route path="/bookmarks" element={<BookmarksPage />} />
+          <Route path="/i/*" element={<ExternalContentPage />} />
 
           {/* NIP-19 route for npub1, note1, naddr1, nevent1, nprofile1 */}
           <Route path="/:nip19" element={<NIP19Page />} />
diff --git a/src/hooks/useBookInfo.ts b/src/hooks/useBookInfo.ts
new file mode 100644
index 00000000..44453a2b
--- /dev/null
+++ b/src/hooks/useBookInfo.ts
@@ -0,0 +1,101 @@
+import { useQuery } from '@tanstack/react-query';
+import { z } from 'zod';
+
+const OpenLibraryBookSchema = z.object({
+  title: z.string(),
+  authors: z.array(z.object({
+    name: z.string(),
+  })).optional(),
+  number_of_pages: z.number().optional(),
+  publish_date: z.string().optional(),
+  publishers: z.array(z.object({
+    name: z.string(),
+  })).optional(),
+  subjects: z.array(z.object({
+    name: z.string(),
+  })).optional(),
+  cover: z.object({
+    small: z.string().optional(),
+    medium: z.string().optional(),
+    large: z.string().optional(),
+  }).optional(),
+  excerpts: z.array(z.object({
+    text: z.string(),
+  })).optional(),
+});
+
+export type BookInfo = z.infer<typeof OpenLibraryBookSchema>;
+
+async function fetchBookInfo(isbn: string, signal?: AbortSignal): Promise<BookInfo | null> {
+  try {
+    const response = await fetch(
+      `https://openlibrary.org/isbn/${isbn}.json`,
+      { signal, headers: { Accept: 'application/json' } },
+    );
+    if (!response.ok) return null;
+
+    const raw = await response.json();
+
+    // OpenLibrary sometimes returns author keys instead of embedded objects.
+    // Fetch author names if needed.
+    let authors: { name: string }[] | undefined;
+    if (raw.authors && Array.isArray(raw.authors)) {
+      const authorEntries = raw.authors as Array<{ key?: string; name?: string }>;
+      const hasKeys = authorEntries.some((a) => a.key && !a.name);
+      if (hasKeys) {
+        const authorNames = await Promise.all(
+          authorEntries.map(async (a) => {
+            if (a.name) return { name: a.name };
+            if (a.key) {
+              try {
+                const res = await fetch(`https://openlibrary.org${a.key}.json`, { signal });
+                if (res.ok) {
+                  const data = await res.json();
+                  return { name: data.name ?? 'Unknown Author' };
+                }
+              } catch { /* ignore */ }
+            }
+            return { name: 'Unknown Author' };
+          }),
+        );
+        authors = authorNames;
+      }
+    }
+
+    // Build cover URLs from cover ID if present
+    let cover: BookInfo['cover'];
+    if (raw.covers && Array.isArray(raw.covers) && raw.covers.length > 0) {
+      const coverId = raw.covers[0];
+      cover = {
+        small: `https://covers.openlibrary.org/b/id/${coverId}-S.jpg`,
+        medium: `https://covers.openlibrary.org/b/id/${coverId}-M.jpg`,
+        large: `https://covers.openlibrary.org/b/id/${coverId}-L.jpg`,
+      };
+    }
+
+    return {
+      title: raw.title ?? 'Unknown Title',
+      authors: authors ?? raw.authors,
+      number_of_pages: raw.number_of_pages,
+      publish_date: raw.publish_date,
+      publishers: raw.publishers,
+      subjects: raw.subjects?.slice(0, 5),
+      cover: cover ?? raw.cover,
+      excerpts: raw.excerpts,
+    };
+  } catch {
+    return null;
+  }
+}
+
+/** Hook to fetch book information from OpenLibrary by ISBN. */
+export function useBookInfo(isbn: string | null) {
+  return useQuery({
+    queryKey: ['book-info', isbn],
+    queryFn: ({ signal }) => fetchBookInfo(isbn!, signal),
+    enabled: !!isbn,
+    staleTime: 1000 * 60 * 60 * 24, // 24 hours
+    gcTime: 1000 * 60 * 60 * 24 * 7, // 7 days
+    retry: 1,
+  });
+}
diff --git a/src/lib/countries.ts b/src/lib/countries.ts
new file mode 100644
index 00000000..e1dcd47c
--- /dev/null
+++ b/src/lib/countries.ts
@@ -0,0 +1,219 @@
+/** ISO 3166-1 alpha-2 country code to country name and flag emoji mapping. */
+export const COUNTRIES: Record<string, { name: string; flag: string }> = {
+  AF: { name: 'Afghanistan', flag: '🇦🇫' },
+  AL: { name: 'Albania', flag: '🇦🇱' },
+  DZ: { name: 'Algeria', flag: '🇩🇿' },
+  AD: { name: 'Andorra', flag: '🇦🇩' },
+  AO: { name: 'Angola', flag: '🇦🇴' },
+  AG: { name: 'Antigua and Barbuda', flag: '🇦🇬' },
+  AR: { name: 'Argentina', flag: '🇦🇷' },
+  AM: { name: 'Armenia', flag: '🇦🇲' },
+  AU: { name: 'Australia', flag: '🇦🇺' },
+  AT: { name: 'Austria', flag: '🇦🇹' },
+  AZ: { name: 'Azerbaijan', flag: '🇦🇿' },
+  BS: { name: 'Bahamas', flag: '🇧🇸' },
+  BH: { name: 'Bahrain', flag: '🇧🇭' },
+  BD: { name: 'Bangladesh', flag: '🇧🇩' },
+  BB: { name: 'Barbados', flag: '🇧🇧' },
+  BY: { name: 'Belarus', flag: '🇧🇾' },
+  BE: { name: 'Belgium', flag: '🇧🇪' },
+  BZ: { name: 'Belize', flag: '🇧🇿' },
+  BJ: { name: 'Benin', flag: '🇧🇯' },
+  BT: { name: 'Bhutan', flag: '🇧🇹' },
+  BO: { name: 'Bolivia', flag: '🇧🇴' },
+  BA: { name: 'Bosnia and Herzegovina', flag: '🇧🇦' },
+  BW: { name: 'Botswana', flag: '🇧🇼' },
+  BR: { name: 'Brazil', flag: '🇧🇷' },
+  BN: { name: 'Brunei', flag: '🇧🇳' },
+  BG: { name: 'Bulgaria', flag: '🇧🇬' },
+  BF: { name: 'Burkina Faso', flag: '🇧🇫' },
+  BI: { name: 'Burundi', flag: '🇧🇮' },
+  CV: { name: 'Cabo Verde', flag: '🇨🇻' },
+  KH: { name: 'Cambodia', flag: '🇰🇭' },
+  CM: { name: 'Cameroon', flag: '🇨🇲' },
+  CA: { name: 'Canada', flag: '🇨🇦' },
+  CF: { name: 'Central African Republic', flag: '🇨🇫' },
+  TD: { name: 'Chad', flag: '🇹🇩' },
+  CL: { name: 'Chile', flag: '🇨🇱' },
+  CN: { name: 'China', flag: '🇨🇳' },
+  CO: { name: 'Colombia', flag: '🇨🇴' },
+  KM: { name: 'Comoros', flag: '🇰🇲' },
+  CG: { name: 'Congo', flag: '🇨🇬' },
+  CD: { name: 'Congo (DRC)', flag: '🇨🇩' },
+  CR: { name: 'Costa Rica', flag: '🇨🇷' },
+  CI: { name: "Cote d'Ivoire", flag: '🇨🇮' },
+  HR: { name: 'Croatia', flag: '🇭🇷' },
+  CU: { name: 'Cuba', flag: '🇨🇺' },
+  CY: { name: 'Cyprus', flag: '🇨🇾' },
+  CZ: { name: 'Czechia', flag: '🇨🇿' },
+  DK: { name: 'Denmark', flag: '🇩🇰' },
+  DJ: { name: 'Djibouti', flag: '🇩🇯' },
+  DM: { name: 'Dominica', flag: '🇩🇲' },
+  DO: { name: 'Dominican Republic', flag: '🇩🇴' },
+  EC: { name: 'Ecuador', flag: '🇪🇨' },
+  EG: { name: 'Egypt', flag: '🇪🇬' },
+  SV: { name: 'El Salvador', flag: '🇸🇻' },
+  GQ: { name: 'Equatorial Guinea', flag: '🇬🇶' },
+  ER: { name: 'Eritrea', flag: '🇪🇷' },
+  EE: { name: 'Estonia', flag: '🇪🇪' },
+  SZ: { name: 'Eswatini', flag: '🇸🇿' },
+  ET: { name: 'Ethiopia', flag: '🇪🇹' },
+  FJ: { name: 'Fiji', flag: '🇫🇯' },
+  FI: { name: 'Finland', flag: '🇫🇮' },
+  FR: { name: 'France', flag: '🇫🇷' },
+  GA: { name: 'Gabon', flag: '🇬🇦' },
+  GM: { name: 'Gambia', flag: '🇬🇲' },
+  GE: { name: 'Georgia', flag: '🇬🇪' },
+  DE: { name: 'Germany', flag: '🇩🇪' },
+  GH: { name: 'Ghana', flag: '🇬🇭' },
+  GR: { name: 'Greece', flag: '🇬🇷' },
+  GD: { name: 'Grenada', flag: '🇬🇩' },
+  GT: { name: 'Guatemala', flag: '🇬🇹' },
+  GN: { name: 'Guinea', flag: '🇬🇳' },
+  GW: { name: 'Guinea-Bissau', flag: '🇬🇼' },
+  GY: { name: 'Guyana', flag: '🇬🇾' },
+  HT: { name: 'Haiti', flag: '🇭🇹' },
+  HN: { name: 'Honduras', flag: '🇭🇳' },
+  HU: { name: 'Hungary', flag: '🇭🇺' },
+  IS: { name: 'Iceland', flag: '🇮🇸' },
+  IN: { name: 'India', flag: '🇮🇳' },
+  ID: { name: 'Indonesia', flag: '🇮🇩' },
+  IR: { name: 'Iran', flag: '🇮🇷' },
+  IQ: { name: 'Iraq', flag: '🇮🇶' },
+  IE: { name: 'Ireland', flag: '🇮🇪' },
+  IL: { name: 'Israel', flag: '🇮🇱' },
+  IT: { name: 'Italy', flag: '🇮🇹' },
+  JM: { name: 'Jamaica', flag: '🇯🇲' },
+  JP: { name: 'Japan', flag: '🇯🇵' },
+  JO: { name: 'Jordan', flag: '🇯🇴' },
+  KZ: { name: 'Kazakhstan', flag: '🇰🇿' },
+  KE: { name: 'Kenya', flag: '🇰🇪' },
+  KI: { name: 'Kiribati', flag: '🇰🇮' },
+  KP: { name: 'North Korea', flag: '🇰🇵' },
+  KR: { name: 'South Korea', flag: '🇰🇷' },
+  KW: { name: 'Kuwait', flag: '🇰🇼' },
+  KG: { name: 'Kyrgyzstan', flag: '🇰🇬' },
+  LA: { name: 'Laos', flag: '🇱🇦' },
+  LV: { name: 'Latvia', flag: '🇱🇻' },
+  LB: { name: 'Lebanon', flag: '🇱🇧' },
+  LS: { name: 'Lesotho', flag: '🇱🇸' },
+  LR: { name: 'Liberia', flag: '🇱🇷' },
+  LY: { name: 'Libya', flag: '🇱🇾' },
+  LI: { name: 'Liechtenstein', flag: '🇱🇮' },
+  LT: { name: 'Lithuania', flag: '🇱🇹' },
+  LU: { name: 'Luxembourg', flag: '🇱🇺' },
+  MG: { name: 'Madagascar', flag: '🇲🇬' },
+  MW: { name: 'Malawi', flag: '🇲🇼' },
+  MY: { name: 'Malaysia', flag: '🇲🇾' },
+  MV: { name: 'Maldives', flag: '🇲🇻' },
+  ML: { name: 'Mali', flag: '🇲🇱' },
+  MT: { name: 'Malta', flag: '🇲🇹' },
+  MH: { name: 'Marshall Islands', flag: '🇲🇭' },
+  MR: { name: 'Mauritania', flag: '🇲🇷' },
+  MU: { name: 'Mauritius', flag: '🇲🇺' },
+  MX: { name: 'Mexico', flag: '🇲🇽' },
+  FM: { name: 'Micronesia', flag: '🇫🇲' },
+  MD: { name: 'Moldova', flag: '🇲🇩' },
+  MC: { name: 'Monaco', flag: '🇲🇨' },
+  MN: { name: 'Mongolia', flag: '🇲🇳' },
+  ME: { name: 'Montenegro', flag: '🇲🇪' },
+  MA: { name: 'Morocco', flag: '🇲🇦' },
+  MZ: { name: 'Mozambique', flag: '🇲🇿' },
+  MM: { name: 'Myanmar', flag: '🇲🇲' },
+  NA: { name: 'Namibia', flag: '🇳🇦' },
+  NR: { name: 'Nauru', flag: '🇳🇷' },
+  NP: { name: 'Nepal', flag: '🇳🇵' },
+  NL: { name: 'Netherlands', flag: '🇳🇱' },
+  NZ: { name: 'New Zealand', flag: '🇳🇿' },
+  NI: { name: 'Nicaragua', flag: '🇳🇮' },
+  NE: { name: 'Niger', flag: '🇳🇪' },
+  NG: { name: 'Nigeria', flag: '🇳🇬' },
+  MK: { name: 'North Macedonia', flag: '🇲🇰' },
+  NO: { name: 'Norway', flag: '🇳🇴' },
+  OM: { name: 'Oman', flag: '🇴🇲' },
+  PK: { name: 'Pakistan', flag: '🇵🇰' },
+  PW: { name: 'Palau', flag: '🇵🇼' },
+  PA: { name: 'Panama', flag: '🇵🇦' },
+  PG: { name: 'Papua New Guinea', flag: '🇵🇬' },
+  PY: { name: 'Paraguay', flag: '🇵🇾' },
+  PE: { name: 'Peru', flag: '🇵🇪' },
+  PH: { name: 'Philippines', flag: '🇵🇭' },
+  PL: { name: 'Poland', flag: '🇵🇱' },
+  PT: { name: 'Portugal', flag: '🇵🇹' },
+  QA: { name: 'Qatar', flag: '🇶🇦' },
+  RO: { name: 'Romania', flag: '🇷🇴' },
+  RU: { name: 'Russia', flag: '🇷🇺' },
+  RW: { name: 'Rwanda', flag: '🇷🇼' },
+  KN: { name: 'Saint Kitts and Nevis', flag: '🇰🇳' },
+  LC: { name: 'Saint Lucia', flag: '🇱🇨' },
+  VC: { name: 'Saint Vincent and the Grenadines', flag: '🇻🇨' },
+  WS: { name: 'Samoa', flag: '🇼🇸' },
+  SM: { name: 'San Marino', flag: '🇸🇲' },
+  ST: { name: 'Sao Tome and Principe', flag: '🇸🇹' },
+  SA: { name: 'Saudi Arabia', flag: '🇸🇦' },
+  SN: { name: 'Senegal', flag: '🇸🇳' },
+  RS: { name: 'Serbia', flag: '🇷🇸' },
+  SC: { name: 'Seychelles', flag: '🇸🇨' },
+  SL: { name: 'Sierra Leone', flag: '🇸🇱' },
+  SG: { name: 'Singapore', flag: '🇸🇬' },
+  SK: { name: 'Slovakia', flag: '🇸🇰' },
+  SI: { name: 'Slovenia', flag: '🇸🇮' },
+  SB: { name: 'Solomon Islands', flag: '🇸🇧' },
+  SO: { name: 'Somalia', flag: '🇸🇴' },
+  ZA: { name: 'South Africa', flag: '🇿🇦' },
+  SS: { name: 'South Sudan', flag: '🇸🇸' },
+  ES: { name: 'Spain', flag: '🇪🇸' },
+  LK: { name: 'Sri Lanka', flag: '🇱🇰' },
+  SD: { name: 'Sudan', flag: '🇸🇩' },
+  SR: { name: 'Suriname', flag: '🇸🇷' },
+  SE: { name: 'Sweden', flag: '🇸🇪' },
+  CH: { name: 'Switzerland', flag: '🇨🇭' },
+  SY: { name: 'Syria', flag: '🇸🇾' },
+  TW: { name: 'Taiwan', flag: '🇹🇼' },
+  TJ: { name: 'Tajikistan', flag: '🇹🇯' },
+  TZ: { name: 'Tanzania', flag: '🇹🇿' },
+  TH: { name: 'Thailand', flag: '🇹🇭' },
+  TL: { name: 'Timor-Leste', flag: '🇹🇱' },
+  TG: { name: 'Togo', flag: '🇹🇬' },
+  TO: { name: 'Tonga', flag: '🇹🇴' },
+  TT: { name: 'Trinidad and Tobago', flag: '🇹🇹' },
+  TN: { name: 'Tunisia', flag: '🇹🇳' },
+  TR: { name: 'Turkey', flag: '🇹🇷' },
+  TM: { name: 'Turkmenistan', flag: '🇹🇲' },
+  TV: { name: 'Tuvalu', flag: '🇹🇻' },
+  UG: { name: 'Uganda', flag: '🇺🇬' },
+  UA: { name: 'Ukraine', flag: '🇺🇦' },
+  AE: { name: 'United Arab Emirates', flag: '🇦🇪' },
+  GB: { name: 'United Kingdom', flag: '🇬🇧' },
+  US: { name: 'United States', flag: '🇺🇸' },
+  UY: { name: 'Uruguay', flag: '🇺🇾' },
+  UZ: { name: 'Uzbekistan', flag: '🇺🇿' },
+  VU: { name: 'Vanuatu', flag: '🇻🇺' },
+  VA: { name: 'Vatican City', flag: '🇻🇦' },
+  VE: { name: 'Venezuela', flag: '🇻🇪' },
+  VN: { name: 'Vietnam', flag: '🇻🇳' },
+  YE: { name: 'Yemen', flag: '🇾🇪' },
+  ZM: { name: 'Zambia', flag: '🇿🇲' },
+  ZW: { name: 'Zimbabwe', flag: '🇿🇼' },
+};
+
+/** Get country info from an ISO 3166 code (country or subdivision). */
+export function getCountryInfo(code: string): { name: string; flag: string; subdivision?: string } | null {
+  const upper = code.toUpperCase();
+
+  // Handle subdivision codes like "US-CA"
+  if (upper.includes('-')) {
+    const [countryCode] = upper.split('-');
+    const country = COUNTRIES[countryCode];
+    if (!country) return null;
+    return {
+      name: country.name,
+      flag: country.flag,
+      subdivision: upper,
+    };
+  }
+
+  const country = COUNTRIES[upper];
+  if (!country) return null;
+  return { name: country.name, flag: country.flag };
+}
diff --git a/src/pages/ExternalContentPage.tsx b/src/pages/ExternalContentPage.tsx
new file mode 100644
index 00000000..ecda495e
--- /dev/null
+++ b/src/pages/ExternalContentPage.tsx
@@ -0,0 +1,413 @@
+import { useMemo } from 'react';
+import { useSeoMeta } from '@unhead/react';
+import { ArrowLeft, BookOpen, ExternalLink, Globe, MapPin } from 'lucide-react';
+import { Link, useParams } from 'react-router-dom';
+import { Skeleton } from '@/components/ui/skeleton';
+import { CommentsSection } from '@/components/comments/CommentsSection';
+import { ExternalFavicon } from '@/components/ExternalFavicon';
+import { useLinkPreview } from '@/hooks/useLinkPreview';
+import { useBookInfo } from '@/hooks/useBookInfo';
+import { getCountryInfo } from '@/lib/countries';
+import { cn, STICKY_HEADER_CLASS } from '@/lib/utils';
+import NotFound from './NotFound';
+
+/** Parsed external content identifier with its type. */
+type ExternalContent =
+  | { type: 'url'; value: string }
+  | { type: 'isbn'; value: string }
+  | { type: 'iso3166'; value: string; code: string }
+  | { type: 'unknown'; value: string };
+
+/** Parse a URI string into a typed external content object. */
+function parseExternalUri(uri: string): ExternalContent {
+  // ISBN - "isbn:9780765382030"
+  if (uri.startsWith('isbn:')) {
+    return { type: 'isbn', value: uri, };
+  }
+
+  // ISO 3166 country/subdivision - "iso3166:US" or "iso3166:US-CA"
+  if (uri.startsWith('iso3166:')) {
+    const code = uri.slice('iso3166:'.length);
+    return { type: 'iso3166', value: uri, code };
+  }
+
+  // URL - starts with http:// or https://
+  if (uri.startsWith('http://') || uri.startsWith('https://')) {
+    return { type: 'url', value: uri };
+  }
+
+  return { type: 'unknown', value: uri };
+}
+
+/** Format an ISBN with hyphens for display (simplified). */
+function formatIsbn(isbn: string): string {
+  const digits = isbn.replace(/\D/g, '');
+  if (digits.length === 13) {
+    return `${digits.slice(0, 3)}-${digits.slice(3, 4)}-${digits.slice(4, 9)}-${digits.slice(9, 12)}-${digits.slice(12)}`;
+  }
+  if (digits.length === 10) {
+    return `${digits.slice(0, 1)}-${digits.slice(1, 5)}-${digits.slice(5, 9)}-${digits.slice(9)}`;
+  }
+  return isbn;
+}
+
+// ---------------------------------------------------------------------------
+// URL content header
+// ---------------------------------------------------------------------------
+
+function UrlContentHeader({ url }: { url: string }) {
+  const { data, isLoading } = useLinkPreview(url);
+
+  const domain = useMemo(() => {
+    try {
+      return new URL(url).hostname.replace(/^www\./, '');
+    } catch {
+      return url;
+    }
+  }, [url]);
+
+  if (isLoading) {
+    return (
+      <div className="rounded-2xl border border-border overflow-hidden">
+        <Skeleton className="w-full h-[220px] rounded-none" />
+        <div className="p-5 space-y-3">
+          <Skeleton className="h-3 w-32" />
+          <Skeleton className="h-6 w-3/4" />
+          <Skeleton className="h-4 w-full" />
+        </div>
+      </div>
+    );
+  }
+
+  const image = data?.thumbnail_url;
+  const title = data?.title;
+  const author = data?.author_name;
+  const providerName = data?.provider_name || domain;
+
+  return (
+    <a
+      href={url}
+      target="_blank"
+      rel="noopener noreferrer"
+      className={cn(
+        'group block rounded-2xl border border-border overflow-hidden',
+        'hover:border-primary/30 hover:shadow-lg hover:shadow-primary/5 transition-all duration-300',
+      )}
+    >
+      {image && (
+        <div className="w-full overflow-hidden">
+          <img
+            src={image}
+            alt=""
+            className="w-full h-[220px] object-cover group-hover:scale-[1.02] transition-transform duration-500"
+            loading="lazy"
+            onError={(e) => {
+              (e.currentTarget.parentElement as HTMLElement).style.display = 'none';
+            }}
+          />
+        </div>
+      )}
+
+      <div className="p-5 space-y-2">
+        <div className="flex items-center gap-2 text-xs text-muted-foreground">
+          <ExternalFavicon url={url} size={14} className="shrink-0" />
+          <span className="truncate">{providerName}</span>
+          <ExternalLink className="size-3 shrink-0 opacity-0 group-hover:opacity-100 transition-opacity" />
+        </div>
+
+        {title && (
+          <h2 className="text-xl font-bold leading-snug line-clamp-3">
+            {title}
+          </h2>
+        )}
+
+        {!title && (
+          <h2 className="text-xl font-bold leading-snug break-all line-clamp-2 text-muted-foreground">
+            {url}
+          </h2>
+        )}
+
+        {author && (
+          <p className="text-sm text-muted-foreground">
+            by {author}
+          </p>
+        )}
+      </div>
+    </a>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Book content header
+// ---------------------------------------------------------------------------
+
+function BookContentHeader({ isbn }: { isbn: string }) {
+  const rawIsbn = isbn.replace('isbn:', '');
+  const { data: book, isLoading } = useBookInfo(rawIsbn);
+  const displayIsbn = formatIsbn(rawIsbn);
+
+  if (isLoading) {
+    return (
+      <div className="rounded-2xl border border-border overflow-hidden p-5">
+        <div className="flex gap-5">
+          <Skeleton className="w-[120px] h-[180px] rounded-lg shrink-0" />
+          <div className="flex-1 space-y-3">
+            <Skeleton className="h-3 w-24" />
+            <Skeleton className="h-6 w-3/4" />
+            <Skeleton className="h-4 w-1/2" />
+            <Skeleton className="h-4 w-1/3" />
+            <div className="flex gap-2 pt-2">
+              <Skeleton className="h-6 w-16 rounded-full" />
+              <Skeleton className="h-6 w-20 rounded-full" />
+            </div>
+          </div>
+        </div>
+      </div>
+    );
+  }
+
+  const coverUrl = book?.cover?.large || book?.cover?.medium;
+  const authors = book?.authors?.map((a) => a.name).join(', ');
+  const publishers = book?.publishers?.map((p) => p.name).join(', ');
+
+  return (
+    <div className="rounded-2xl border border-border overflow-hidden">
+      <div className="p-5">
+        <div className="flex gap-5">
+          {/* Book cover */}
+          {coverUrl ? (
+            <div className="shrink-0">
+              <img
+                src={coverUrl}
+                alt={book?.title || 'Book cover'}
+                className="w-[120px] sm:w-[140px] rounded-lg shadow-md object-cover"
+                loading="lazy"
+                onError={(e) => {
+                  (e.currentTarget as HTMLElement).style.display = 'none';
+                }}
+              />
+            </div>
+          ) : (
+            <div className="shrink-0 w-[120px] sm:w-[140px] h-[180px] sm:h-[210px] rounded-lg bg-secondary flex items-center justify-center">
+              <BookOpen className="size-10 text-muted-foreground/40" />
+            </div>
+          )}
+
+          {/* Book details */}
+          <div className="flex-1 min-w-0 space-y-2">
+            <div className="flex items-center gap-1.5 text-xs text-muted-foreground">
+              <BookOpen className="size-3.5 shrink-0" />
+              <span>ISBN {displayIsbn}</span>
+            </div>
+
+            <h2 className="text-xl font-bold leading-snug line-clamp-3">
+              {book?.title || 'Unknown Book'}
+            </h2>
+
+            {authors && (
+              <p className="text-sm text-muted-foreground">
+                by {authors}
+              </p>
+            )}
+
+            <div className="flex flex-wrap items-center gap-x-4 gap-y-1 text-xs text-muted-foreground pt-1">
+              {book?.publish_date && (
+                <span>{book.publish_date}</span>
+              )}
+              {publishers && (
+                <span>{publishers}</span>
+              )}
+              {book?.number_of_pages && (
+                <span>{book.number_of_pages} pages</span>
+              )}
+            </div>
+
+            {book?.subjects && book.subjects.length > 0 && (
+              <div className="flex flex-wrap gap-1.5 pt-2">
+                {book.subjects.map((s) => (
+                  <span
+                    key={s.name}
+                    className="text-xs px-2.5 py-0.5 rounded-full bg-secondary text-muted-foreground"
+                  >
+                    {s.name}
+                  </span>
+                ))}
+              </div>
+            )}
+          </div>
+        </div>
+      </div>
+
+      {/* OpenLibrary link */}
+      <div className="border-t border-border px-5 py-2.5">
+        <a
+          href={`https://openlibrary.org/isbn/${rawIsbn}`}
+          target="_blank"
+          rel="noopener noreferrer"
+          className="flex items-center gap-1.5 text-xs text-muted-foreground hover:text-foreground transition-colors"
+        >
+          <Globe className="size-3.5" />
+          <span>View on OpenLibrary</span>
+          <ExternalLink className="size-3" />
+        </a>
+      </div>
+    </div>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Country content header
+// ---------------------------------------------------------------------------
+
+function CountryContentHeader({ code }: { code: string }) {
+  const info = getCountryInfo(code);
+
+  if (!info) {
+    return (
+      <div className="rounded-2xl border border-border p-5 text-center">
+        <MapPin className="size-8 mx-auto mb-2 text-muted-foreground/40" />
+        <p className="text-muted-foreground">Unknown country code: {code}</p>
+      </div>
+    );
+  }
+
+  return (
+    <div className="rounded-2xl border border-border overflow-hidden">
+      <div className="p-6 sm:p-8">
+        <div className="flex items-center gap-4">
+          <span className="text-6xl sm:text-7xl leading-none" role="img" aria-label={`Flag of ${info.name}`}>
+            {info.flag}
+          </span>
+          <div className="space-y-1">
+            <div className="flex items-center gap-1.5 text-xs text-muted-foreground">
+              <MapPin className="size-3.5 shrink-0" />
+              <span>ISO 3166 {info.subdivision ? `(${info.subdivision})` : `(${code.toUpperCase()})`}</span>
+            </div>
+            <h2 className="text-2xl sm:text-3xl font-bold leading-snug">
+              {info.name}
+            </h2>
+            {info.subdivision && (
+              <p className="text-sm text-muted-foreground">
+                Subdivision: {info.subdivision}
+              </p>
+            )}
+          </div>
+        </div>
+      </div>
+
+      <div className="border-t border-border px-5 py-2.5">
+        <a
+          href={`https://en.wikipedia.org/wiki/ISO_3166-2:${code.toUpperCase()}`}
+          target="_blank"
+          rel="noopener noreferrer"
+          className="flex items-center gap-1.5 text-xs text-muted-foreground hover:text-foreground transition-colors"
+        >
+          <Globe className="size-3.5" />
+          <span>View on Wikipedia</span>
+          <ExternalLink className="size-3" />
+        </a>
+      </div>
+    </div>
+  );
+}
+
+// ---------------------------------------------------------------------------
+// Page header label
+// ---------------------------------------------------------------------------
+
+function headerLabel(content: ExternalContent): string {
+  switch (content.type) {
+    case 'url':
+      try {
+        return new URL(content.value).hostname.replace(/^www\./, '');
+      } catch {
+        return 'Web Page';
+      }
+    case 'isbn':
+      return 'Book';
+    case 'iso3166':
+      return getCountryInfo(content.code)?.name ?? 'Country';
+    default:
+      return 'External Content';
+  }
+}
+
+function seoTitle(content: ExternalContent): string {
+  switch (content.type) {
+    case 'url':
+      try {
+        return `${new URL(content.value).hostname.replace(/^www\./, '')} | Ditto`;
+      } catch {
+        return 'Web Page | Ditto';
+      }
+    case 'isbn': {
+      const isbn = content.value.replace('isbn:', '');
+      return `Book (ISBN ${isbn}) | Ditto`;
+    }
+    case 'iso3166': {
+      const info = getCountryInfo(content.code);
+      return info ? `${info.name} | Ditto` : 'Country | Ditto';
+    }
+    default:
+      return 'External Content | Ditto';
+  }
+}
+
+// ---------------------------------------------------------------------------
+// Main page component
+// ---------------------------------------------------------------------------
+
+export function ExternalContentPage() {
+  const { '*': rawUri } = useParams();
+  const uri = rawUri ? decodeURIComponent(rawUri) : '';
+
+  const content = useMemo(() => {
+    if (!uri) return null;
+    return parseExternalUri(uri);
+  }, [uri]);
+
+  useSeoMeta({ title: content ? seoTitle(content) : 'External Content | Ditto' });
+
+  if (!content || !uri) {
+    return <NotFound />;
+  }
+
+  // Build the NIP-73 identifier for comments.
+  // For URLs, the raw URL is used. For others, the full prefixed identifier.
+  const commentRoot = useMemo(() => {
+    return new URL(content.value);
+  }, [content.value]);
+
+  return (
+    <main className="min-h-screen">
+      {/* Sticky header */}
+      <div className={cn(STICKY_HEADER_CLASS, 'flex items-center gap-4 px-4 mt-4 mb-5 bg-background/80 backdrop-blur-md z-10')}>
+        <Link to="/" className="p-2 rounded-full hover:bg-secondary transition-colors sidebar:hidden">
+          <ArrowLeft className="size-5" />
+        </Link>
+        <h1 className="text-xl font-bold truncate">{headerLabel(content)}</h1>
+      </div>
+
+      <div className="px-4 space-y-6 pb-8">
+        {/* Content-specific header */}
+        {content.type === 'url' && <UrlContentHeader url={content.value} />}
+        {content.type === 'isbn' && <BookContentHeader isbn={content.value} />}
+        {content.type === 'iso3166' && <CountryContentHeader code={content.code} />}
+        {content.type === 'unknown' && (
+          <div className="rounded-2xl border border-border p-5 text-center">
+            <Globe className="size-8 mx-auto mb-2 text-muted-foreground/40" />
+            <p className="text-sm text-muted-foreground break-all">{content.value}</p>
+          </div>
+        )}
+
+        {/* Comments section */}
+        <CommentsSection
+          root={commentRoot}
+          title="Discussion"
+          emptyStateMessage="No comments yet"
+          emptyStateSubtitle="Be the first to share your thoughts about this!"
+        />
+      </div>
+    </main>
+  );
+}