diff --git a/README.md b/README.md
index ddb9199..f03512f 100644
--- a/README.md
+++ b/README.md
@@ -105,7 +105,7 @@ The backend starts on port 3001, initializes the database, and begins the cron s
 npm run dev
 ```
 
-Open [http://localhost:3000](http://localhost:3000). Navigate weeks with the `←` / `→` buttons, or pass `?week=YYYY-MM-DD` directly. Click any park name to open its detail page.
+Open [http://localhost:3000](http://localhost:3000). Navigate weeks with the `←` / `→` buttons (or arrow keys); your selected week persists across visits via the `tcWeek` cookie. Click any park name to open its detail page.
 
 ### Debug a specific park + date
 
diff --git a/app/actions/week.ts b/app/actions/week.ts
new file mode 100644
index 0000000..42784ce
--- /dev/null
+++ b/app/actions/week.ts
@@ -0,0 +1,29 @@
+"use server";
+
+import { cookies } from "next/headers";
+import { revalidatePath } from "next/cache";
+
+const WEEK_COOKIE = "tcWeek";
+const MAX_AGE = 60 * 60 * 24 * 30; // 30 days
+
+/**
+ * Persist the selected week start (YYYY-MM-DD) in a server-readable cookie
+ * and revalidate the home page so the new week renders.
+ */
+export async function setWeek(weekStart: string): Promise<void> {
+  if (!/^\d{4}-\d{2}-\d{2}$/.test(weekStart)) return;
+  const cookieStore = await cookies();
+  cookieStore.set(WEEK_COOKIE, weekStart, {
+    path: "/",
+    maxAge: MAX_AGE,
+    sameSite: "lax",
+  });
+  revalidatePath("/");
+}
+
+/** Clear the saved week — used by the "Today" button to jump back to current. */
+export async function clearWeek(): Promise<void> {
+  const cookieStore = await cookies();
+  cookieStore.delete(WEEK_COOKIE);
+  revalidatePath("/");
+}
diff --git a/app/page.tsx b/app/page.tsx
index 14d7545..423b82c 100644
--- a/app/page.tsx
+++ b/app/page.tsx
@@ -1,15 +1,14 @@
+import { cookies } from "next/headers";
 import { HomePageClient } from "@/components/HomePageClient";
 import { getTodayLocal, formatDateLocal } from "@/lib/env";
 
 const BACKEND_URL = process.env.BACKEND_URL ?? "http://localhost:3001";
 
-interface PageProps {
-  searchParams: Promise<{ week?: string }>;
-}
+const WEEK_COOKIE = "tcWeek";
 
-function getWeekStart(param: string | undefined): string {
-  if (param && /^\d{4}-\d{2}-\d{2}$/.test(param)) {
-    const d = new Date(param + "T00:00:00");
+function getWeekStart(saved: string | undefined): string {
+  if (saved && /^\d{4}-\d{2}-\d{2}$/.test(saved)) {
+    const d = new Date(saved + "T00:00:00");
     if (!isNaN(d.getTime())) {
       d.setDate(d.getDate() - d.getDay());
       return formatDateLocal(d);
@@ -21,9 +20,9 @@ function getWeekStart(param: string | undefined): string {
   return formatDateLocal(d);
 }
 
-export default async function HomePage({ searchParams }: PageProps) {
-  const params = await searchParams;
-  const weekStart = getWeekStart(params.week);
+export default async function HomePage() {
+  const saved = (await cookies()).get(WEEK_COOKIE)?.value;
+  const weekStart = getWeekStart(saved);
 
   const data = await fetch(
     `${BACKEND_URL}/api/calendar/week?start=${weekStart}`,
diff --git a/components/BackToCalendarLink.tsx b/components/BackToCalendarLink.tsx
index 5fe3d03..557927b 100644
--- a/components/BackToCalendarLink.tsx
+++ b/components/BackToCalendarLink.tsx
@@ -1,19 +1,12 @@
-"use client";
-
-import { useState, useEffect } from "react";
 import Link from "next/link";
 
 export function BackToCalendarLink() {
-  const [href, setHref] = useState("/");
-
-  useEffect(() => {
-    const saved = localStorage.getItem("lastWeek");
-    if (saved) setHref(`/?week=${saved}`);
-  }, []);
-
+  // The selected week is stored in a server-readable cookie (tcWeek), so the
+  // home page already renders the right week without us needing to pass it
+  // through the URL.
   return (
     <Link
-      href={href}
+      href="/"
       className="park-name-link"
       style={{
         display: "flex",
diff --git a/components/HomePageClient.tsx b/components/HomePageClient.tsx
index ba2f425..4609456 100644
--- a/components/HomePageClient.tsx
+++ b/components/HomePageClient.tsx
@@ -109,11 +109,6 @@ export function HomePageClient({
     return () => timeouts.forEach(clearTimeout);
   }, [isCurrentWeek, today, data, router]);
 
-  // Remember the current week so the park page back button returns here.
-  useEffect(() => {
-    localStorage.setItem("lastWeek", weekStart);
-  }, [weekStart]);
-
   const toggle = () => {
     const next = !coastersOnly;
     setCoastersOnly(next);
diff --git a/components/WeekNav.tsx b/components/WeekNav.tsx
index 7437658..1fe192b 100644
--- a/components/WeekNav.tsx
+++ b/components/WeekNav.tsx
@@ -1,7 +1,7 @@
 "use client";
 
 import { useEffect } from "react";
-import { useRouter } from "next/navigation";
+import { setWeek, clearWeek } from "@/app/actions/week";
 
 interface WeekNavProps {
   weekStart: string;   // YYYY-MM-DD (Sunday)
@@ -39,9 +39,11 @@ function shiftWeek(weekStart: string, delta: number): string {
 }
 
 export function WeekNav({ weekStart, weekDates, isCurrentWeek }: WeekNavProps) {
-  const router = useRouter();
   const nav = (delta: number) => {
-    router.push(`/?week=${shiftWeek(weekStart, delta)}`);
+    void setWeek(shiftWeek(weekStart, delta));
+  };
+  const jumpToToday = () => {
+    void clearWeek();
   };
 
   useEffect(() => {
@@ -68,7 +70,7 @@ export function WeekNav({ weekStart, weekDates, isCurrentWeek }: WeekNavProps) {
 
       {!isCurrentWeek && (
         <button
-          onClick={() => router.push("/")}
+          onClick={jumpToToday}
           aria-label="Jump to current week"
           style={todayBtnStyle}
           onMouseOver={(e) => Object.assign((e.target as HTMLElement).style, todayBtnHover)}
diff --git a/docs/ARCHITECTURE.md b/docs/ARCHITECTURE.md
index beb578e..1e9f73d 100644
--- a/docs/ARCHITECTURE.md
+++ b/docs/ARCHITECTURE.md
@@ -420,12 +420,18 @@ park/[id]/page.tsx (Server)
 2. **Opening-time refresh**: For each park open today, calculates milliseconds until its opening time using `msUntilLocalTime()` (timezone-aware). Schedules `router.refresh()` at opening and again 30 seconds later (to pick up ride counts after Queue-Times starts reporting).
 3. **Keyboard navigation**: Left/right arrow keys navigate between weeks (via `WeekNav` component).
 
+### Cookies
+
+| Name | Purpose |
+|------|---------|
+| `tcWeek` | Selected week start date (`YYYY-MM-DD`). Set by `WeekNav` and read server-side by `app/page.tsx`, so the home page renders the right week without polluting the URL. |
+
 ### localStorage
 
 | Key | Purpose |
 |-----|---------|
-| `lastWeek` | Remembers the last viewed week start date, used by `BackToCalendarLink` to return to the correct week |
 | `coasterMode` | Persists the "Coasters only" toggle state across sessions |
+| `fastLaneMode` | Persists the Fast Lane wait toggle on the park page |
 
 ### Responsive Design
 
diff --git a/docs/DEVELOPMENT.md b/docs/DEVELOPMENT.md
index 3bd7156..39c819e 100644
--- a/docs/DEVELOPMENT.md
+++ b/docs/DEVELOPMENT.md
@@ -55,7 +55,7 @@ npm run dev
 This starts the Next.js dev server on port 3000 with hot reload. Open [http://localhost:3000](http://localhost:3000).
 
 **Navigation:**
-- Use the `←` / `→` buttons to navigate weeks, or pass `?week=YYYY-MM-DD` in the URL
+- Use the `←` / `→` buttons (or arrow keys) to navigate weeks; the selected week persists across visits via the `tcWeek` cookie
 - Click any park name to open its detail page with month calendar and ride status
 
 ---