diff --git a/DECISIONS.md b/DECISIONS.md
index 4254c28..843d82a 100644
--- a/DECISIONS.md
+++ b/DECISIONS.md
@@ -288,3 +288,8 @@ Implementation decisions not spelled out in `memory-bank/implementation-plan.md`
 - **Ship names** are "Adjective Noun" from fixed word lists, picked by a generator seeded with `deriveSeed(worldSeed, "ship-name:<n>")`, where n is how many ships the player owned before this one. They are stable per world (decision 0.5.14) and are not unique; duplicates are acceptable. Word lists live in the server (`src/game/names.ts`) because they are not tuning numbers.
 - **New ships always appear at Earth**, as the plan says, whatever the player's bays.
 - **`spend()` checks and deducts credits inside the player lock**, so a failed purchase changes nothing (`409 insufficient-funds`). Unknown models return `404 not-found`.
+
+## Step 6.6
+
+- **A bay lease is a one-time payment** of the location's `bayLeasePrice`, as the plan words it ("one-time lease price"); there is no recurring rent in the base game.
+- **Check order:** location exists (`404 not-found`), discovered (`409 location-undiscovered`), no bay there yet (`409 bay-already-leased`), affordable (`409 insufficient-funds`).
diff --git a/apps/server/src/game/fleet.ts b/apps/server/src/game/fleet.ts
index a49be70..ccbf2b6 100644
--- a/apps/server/src/game/fleet.ts
+++ b/apps/server/src/game/fleet.ts
@@ -1,10 +1,10 @@
 import { randomUUID } from "node:crypto";
 import { content } from "@deadhead/content";
-import type { Ship } from "@deadhead/schema";
+import type { Bay, Ship } from "@deadhead/schema";
 import type { RealTime } from "@deadhead/sim";
-import { count, eq, sql } from "drizzle-orm";
+import { and, count, eq, sql } from "drizzle-orm";
 import type { Queryable } from "../db/client";
-import { companies, players, ships } from "../db/schema";
+import { bays, companies, discoveredLocations, players, ships } from "../db/schema";
 import { gameError } from "../http/errors";
 import { shipName } from "./names";
 
@@ -35,6 +35,46 @@ export async function spend(tx: Queryable, playerId: string, amount: number, wha
     .where(eq(companies.playerId, playerId));
 }
 
+/** Leases a bay at a discovered location for its one-time price (Step 6.6). */
+export async function leaseBay(
+  tx: Queryable,
+  playerId: string,
+  locationId: string,
+  now: RealTime,
+): Promise<Bay> {
+  const location = content.location(locationId);
+  if (!location) throw gameError("not-found", `No location "${locationId}".`);
+
+  const [discovered] = await tx
+    .select()
+    .from(discoveredLocations)
+    .where(
+      and(
+        eq(discoveredLocations.playerId, playerId),
+        eq(discoveredLocations.locationId, locationId),
+      ),
+    );
+  if (!discovered) {
+    throw gameError(
+      "location-undiscovered",
+      `Deliver to ${location.name} before leasing a bay there.`,
+    );
+  }
+  const [existing] = await tx
+    .select()
+    .from(bays)
+    .where(and(eq(bays.playerId, playerId), eq(bays.locationId, locationId)));
+  if (existing)
+    throw gameError("bay-already-leased", `You already have a bay at ${location.name}.`);
+
+  await spend(tx, playerId, location.bayLeasePrice, `a bay at ${location.name}`);
+  const [bay] = await tx
+    .insert(bays)
+    .values({ id: randomUUID(), playerId, locationId, createdAt: now })
+    .returning();
+  return { id: bay!.id, locationId: bay!.locationId };
+}
+
 /** Buys a ship model: it appears idle at Earth with no pilot (Step 6.5). */
 export async function buyShip(
   tx: Queryable,
diff --git a/apps/server/src/routes/fleet.ts b/apps/server/src/routes/fleet.ts
index fc9a9f6..5bf204f 100644
--- a/apps/server/src/routes/fleet.ts
+++ b/apps/server/src/routes/fleet.ts
@@ -1,6 +1,6 @@
 import { routes } from "@deadhead/schema";
 import type { FastifyInstance } from "fastify";
-import { buyShip } from "../game/fleet";
+import { buyShip, leaseBay } from "../game/fleet";
 import { registerRoute } from "../http/route";
 import type { AppContext } from "./context";
 import { withPlayer } from "./with-player";
@@ -12,4 +12,10 @@ export function registerFleetRoutes(app: FastifyInstance, ctx: AppContext): void
       ship: await buyShip(tx, playerId, input.modelId, now),
     })),
   );
+
+  registerRoute(app, routes.leaseBay, ctx.options, async (input, { playerId }) =>
+    withPlayer(ctx, playerId, async (tx, now) => ({
+      bay: await leaseBay(tx, playerId, input.locationId, now),
+    })),
+  );
 }
diff --git a/apps/server/test/lease-bay.test.ts b/apps/server/test/lease-bay.test.ts
new file mode 100644
index 0000000..d502b8c
--- /dev/null
+++ b/apps/server/test/lease-bay.test.ts
@@ -0,0 +1,63 @@
+import { content } from "@deadhead/content";
+import { bayResponseSchema, errorResponseSchema } from "@deadhead/schema";
+import { describe, expect, it } from "vitest";
+import { setCredits, useTestDatabase } from "./db";
+import { call, getState, signUp, useTestApp } from "./game";
+
+const database = useTestDatabase();
+const testApp = useTestApp(database);
+
+const errorCode = (response: { json(): unknown }) =>
+  errorResponseSchema.parse(response.json()).error.code;
+
+describe("lease a bay", () => {
+  it("leases a bay at Earth and deducts the price", async () => {
+    const { app } = testApp();
+    const guest = await signUp(app);
+    const price = content.location("earth")!.bayLeasePrice;
+    await setCredits(database().db, guest.playerId, price + 100);
+
+    const response = await call(app, guest, "POST", "/api/bays", { locationId: "earth" });
+    expect(response.statusCode).toBe(200);
+    const { bay } = bayResponseSchema.parse(response.json());
+    expect(bay.locationId).toBe("earth");
+
+    const state = await getState(app, guest);
+    expect(state.company.credits).toBe(100);
+    expect(state.bays).toEqual([bay]);
+  });
+
+  it("refuses an undiscovered location", async () => {
+    const { app } = testApp();
+    const guest = await signUp(app);
+    await setCredits(database().db, guest.playerId, 1_000_000);
+    const response = await call(app, guest, "POST", "/api/bays", { locationId: "mars" });
+    expect(response.statusCode).toBe(409);
+    expect(errorCode(response)).toBe("location-undiscovered");
+    expect((await getState(app, guest)).company.credits).toBe(1_000_000);
+  });
+
+  it("refuses a second bay at the same location", async () => {
+    const { app } = testApp();
+    const guest = await signUp(app);
+    await setCredits(database().db, guest.playerId, 1_000_000);
+    await call(app, guest, "POST", "/api/bays", { locationId: "moon" });
+    const response = await call(app, guest, "POST", "/api/bays", { locationId: "moon" });
+    expect(response.statusCode).toBe(409);
+    expect(errorCode(response)).toBe("bay-already-leased");
+    const state = await getState(app, guest);
+    expect(state.bays).toHaveLength(1);
+    expect(state.company.credits).toBe(1_000_000 - content.location("moon")!.bayLeasePrice);
+  });
+
+  it("refuses when the player cannot afford it, and unknown locations", async () => {
+    const { app } = testApp();
+    const guest = await signUp(app);
+    await setCredits(database().db, guest.playerId, 0);
+    expect(errorCode(await call(app, guest, "POST", "/api/bays", { locationId: "earth" }))).toBe(
+      "insufficient-funds",
+    );
+    const unknown = await call(app, guest, "POST", "/api/bays", { locationId: "pluto" });
+    expect(unknown.statusCode).toBe(404);
+  });
+});
diff --git a/memory-bank/progress.md b/memory-bank/progress.md
index d2bd36b..1cba761 100644
--- a/memory-bank/progress.md
+++ b/memory-bank/progress.md
@@ -59,7 +59,7 @@
 - [x] **Step 6.3 — Tutorial board endpoint.** `GET /api/tutorial/board` (`src/routes/boards.ts`, `src/game/boards.ts`): stored per (period, loaner location) on first request, accepted contracts hidden, `409 not-in-tutorial` after the tutorial. Every game route now runs through `withPlayer` (lock + lazy resolution).
 - [x] **Step 6.4 — Tutorial dispatch.** `POST /api/dispatches` with `kind: "tutorial"` (`src/game/dispatch.ts`): avatar + loaner, sim validation, no fuel, one run at a time; contract marked accepted. Arrival pays the stored tutorial payout and moves loaner and avatar.
 - [x] **Step 6.5 — Buy a ship.** `POST /api/ships` (`src/game/fleet.ts`, `src/routes/fleet.ts`): deducts the price, adds an idle uncrewed ship at Earth named from the world seed (`src/game/names.ts`); `409 insufficient-funds` changes nothing.
-- [ ] Step 6.6 — Lease a bay
+- [x] **Step 6.6 — Lease a bay.** `POST /api/bays` (`leaseBay` in `src/game/fleet.ts`): one-time lease price at a discovered location; `409 location-undiscovered`, `409 bay-already-leased`, `409 insufficient-funds`, `404 not-found`.
 - [ ] Step 6.7 — End tutorial
 - [ ] Step 6.8 — Hire and assign pilots
 - [ ] Step 6.9 — Bay contract board endpoint