diff --git a/src/app/not-found.tsx b/src/app/not-found.tsx
new file mode 100644
index 0000000..0c08cf9
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+++ b/src/app/not-found.tsx
@@ -0,0 +1,142 @@
+'use client';
+
+import Link from 'next/link';
+import { motion } from 'framer-motion';
+import { ArrowLeft, Leaf, Telescope } from 'lucide-react';
+import Header from '@/components/Header';
+import SearchBox from '@/components/explore/SearchBox';
+
+/**
+ * Global 404 page. Next.js falls back to its plain-text default when this
+ * file is absent; this version mirrors the site's hero treatment so a
+ * mistyped URL doesn't read as a regression to a different product.
+ *
+ * Bias toward "give the visitor a way out": leaf-anchored eyebrow, big
+ * serif headline, two-line explainer, the explorer's SearchBox (so a
+ * fat-fingered handle is one re-keystroke away from working), and a Home
+ * button next to a /explore link.
+ */
+export default function NotFound() {
+  return (
+    <div style={{ position: 'relative', overflow: 'hidden' }}>
+      <div className="container-narrow" style={{ padding: '2rem 2rem 0' }}>
+        <Header compact />
+      </div>
+
+      <motion.section
+        initial={{ opacity: 0, y: 16 }}
+        animate={{ opacity: 1, y: 0 }}
+        transition={{ duration: 0.5, ease: [0.34, 1.56, 0.64, 1] }}
+        style={{
+          maxWidth: '40rem',
+          margin: '3rem auto 4rem',
+          padding: '0 2rem',
+        }}
+      >
+        {/* Eyebrow */}
+        <div
+          style={{
+            display: 'inline-flex',
+            alignItems: 'center',
+            gap: '0.5rem',
+            padding: '0.3rem 0.7rem',
+            border: '1px solid var(--border-subtle)',
+            background: 'var(--bg-tertiary)',
+            color: 'var(--text-tertiary)',
+            fontSize: '0.7rem',
+            letterSpacing: '0.12em',
+            textTransform: 'uppercase',
+            fontFamily: 'var(--font-serif)',
+            marginBottom: '1.25rem',
+            transform: 'rotate(-0.4deg)',
+          }}
+        >
+          <Leaf size={11} aria-hidden style={{ color: 'var(--text-accent)' }} />
+          404 · Not found
+        </div>
+
+        <h1
+          style={{
+            fontSize: '2.75rem',
+            fontWeight: 300,
+            letterSpacing: '-0.02em',
+            color: 'var(--text-primary)',
+            marginBottom: '0.75rem',
+            lineHeight: 1.05,
+          }}
+        >
+          <span
+            style={{
+              background:
+                'linear-gradient(135deg, var(--text-primary) 0%, var(--text-accent) 100%)',
+              WebkitBackgroundClip: 'text',
+              WebkitTextFillColor: 'transparent',
+              backgroundClip: 'text',
+            }}
+          >
+            Lost in the Atmosphere.
+          </span>
+        </h1>
+
+        <p
+          style={{
+            fontSize: '1.0625rem',
+            color: 'var(--text-secondary)',
+            lineHeight: 1.6,
+            marginBottom: '1.5rem',
+          }}
+        >
+          The path you tried didn&rsquo;t resolve. Search for a handle, DID, or
+          AT URI to keep looking — or head home.
+        </p>
+
+        {/* Search */}
+        <div style={{ marginBottom: '1.25rem' }}>
+          <SearchBox />
+        </div>
+
+        {/* Quick actions */}
+        <div
+          style={{
+            display: 'flex',
+            flexWrap: 'wrap',
+            gap: '0.625rem',
+          }}
+        >
+          <Link href="/" style={primaryBtn}>
+            <ArrowLeft size={14} aria-hidden /> Home
+          </Link>
+          <Link href="/explore" style={ghostBtn}>
+            <Telescope size={14} aria-hidden /> Explore
+          </Link>
+        </div>
+      </motion.section>
+    </div>
+  );
+}
+
+const primaryBtn: React.CSSProperties = {
+  display: 'inline-flex',
+  alignItems: 'center',
+  gap: '0.4rem',
+  padding: '0.55rem 1rem',
+  background: 'var(--accent-moss)',
+  color: 'var(--text-on-accent)',
+  border: '1px solid var(--accent-moss)',
+  fontFamily: 'var(--font-serif)',
+  fontSize: '0.875rem',
+  textDecoration: 'none',
+};
+
+const ghostBtn: React.CSSProperties = {
+  display: 'inline-flex',
+  alignItems: 'center',
+  gap: '0.4rem',
+  padding: '0.55rem 1rem',
+  background: 'var(--bg-tertiary)',
+  color: 'var(--text-primary)',
+  border: '1px solid var(--border-medium)',
+  fontFamily: 'var(--font-serif)',
+  fontSize: '0.875rem',
+  textDecoration: 'none',
+};