diff --git a/src/map.lua b/src/map.lua
new file mode 100644
index 0000000..1d3e9ac
--- /dev/null
+++ b/src/map.lua
@@ -0,0 +1,175 @@
+-- Level grid: walls, floors, stairs, doors, traps and other terrain. Tile
+-- semantics (walkable, blocks sight, is a door) live in the Tiles registry;
+-- the default generator places random non-overlapping rooms and links their
+-- centres with L-shaped corridors.
+
+local Tiles = require("tiles")
+
+local Map = {}
+Map.__index = Map
+
+Map.WALL = Tiles.WALL
+Map.FLOOR = Tiles.FLOOR
+Map.STAIRS = Tiles.STAIRS_DOWN
+Map.STAIRS_DOWN = Tiles.STAIRS_DOWN
+Map.STAIRS_UP = Tiles.STAIRS_UP
+Map.DOOR_CLOSED = Tiles.DOOR_CLOSED
+Map.DOOR_OPEN = Tiles.DOOR_OPEN
+Map.DOOR_LOCKED = Tiles.DOOR_LOCKED
+Map.TRAP = Tiles.TRAP
+Map.WATER = Tiles.WATER
+
+local function newGrid(width, height, fill)
+  local tiles = {}
+  for i = 1, width * height do
+    tiles[i] = fill
+  end
+  return tiles
+end
+
+function Map.new(width, height)
+  return setmetatable({
+    width = width,
+    height = height,
+    tiles = newGrid(width, height, Map.WALL),
+    rooms = {},
+    stairsX = 0, stairsY = 0,
+    startX = 0, startY = 0,
+  }, Map)
+end
+
+function Map:index(x, y)
+  return (y - 1) * self.width + x
+end
+
+function Map:inBounds(x, y)
+  return x >= 1 and y >= 1 and x <= self.width and y <= self.height
+end
+
+function Map:get(x, y)
+  if not self:inBounds(x, y) then return Map.WALL end
+  return self.tiles[self:index(x, y)]
+end
+
+function Map:set(x, y, tile)
+  self.tiles[self:index(x, y)] = tile
+end
+
+function Map:isWalkable(x, y)
+  return Tiles.isWalkable(self:get(x, y))
+end
+
+function Map:blocksSight(x, y)
+  return Tiles.blocksSight(self:get(x, y))
+end
+
+-- Passability for pathing: closed doors count as passable so routes lead through
+-- them; a locked door is only passable when the traveller holds a key.
+function Map:isPassable(x, y, hasKey)
+  local tile = self:get(x, y)
+  if Tiles.isWalkable(tile) then return true end
+  if tile == Map.DOOR_CLOSED then return true end
+  if tile == Map.DOOR_LOCKED then return hasKey == true end
+  return false
+end
+
+local function carveRoom(map, room)
+  for y = room.y, room.y + room.h - 1 do
+    for x = room.x, room.x + room.w - 1 do
+      map:set(x, y, Map.FLOOR)
+    end
+  end
+end
+
+local function carveHTunnel(map, x1, x2, y)
+  for x = math.min(x1, x2), math.max(x1, x2) do
+    map:set(x, y, Map.FLOOR)
+  end
+end
+
+local function carveVTunnel(map, y1, y2, x)
+  for y = math.min(y1, y2), math.max(y1, y2) do
+    map:set(x, y, Map.FLOOR)
+  end
+end
+
+local function roomsOverlap(a, b)
+  return a.x <= b.x + b.w and a.x + a.w >= b.x
+     and a.y <= b.y + b.h and a.y + a.h >= b.y
+end
+
+local function roomCenter(room)
+  return room.x + room.w // 2, room.y + room.h // 2
+end
+
+function Map.generate(width, height, rng, options)
+  options = options or {}
+  local maxRooms = options.maxRooms or 12
+  local minSize = options.minRoomSize or 4
+  local maxSize = options.maxRoomSize or 8
+  local map = Map.new(width, height)
+
+  for _ = 1, maxRooms do
+    local w = rng:range(minSize, maxSize)
+    local h = rng:range(minSize, maxSize)
+    local room = {
+      x = rng:range(2, width - w - 1),
+      y = rng:range(2, height - h - 1),
+      w = w, h = h,
+    }
+    local fits = true
+    for _, other in ipairs(map.rooms) do
+      if roomsOverlap(room, other) then
+        fits = false
+        break
+      end
+    end
+    if fits then
+      carveRoom(map, room)
+      if #map.rooms > 0 then
+        local prevX, prevY = roomCenter(map.rooms[#map.rooms])
+        local newX, newY = roomCenter(room)
+        if rng:chance(1, 2) then
+          carveHTunnel(map, prevX, newX, prevY)
+          carveVTunnel(map, prevY, newY, newX)
+        else
+          carveVTunnel(map, prevY, newY, prevX)
+          carveHTunnel(map, prevX, newX, newY)
+        end
+      end
+      map.rooms[#map.rooms + 1] = room
+    end
+  end
+
+  map.startX, map.startY = roomCenter(map.rooms[1])
+  map.stairsX, map.stairsY = roomCenter(map.rooms[#map.rooms])
+  map:set(map.stairsX, map.stairsY, Map.STAIRS)
+  return map
+end
+
+function Map:toData()
+  return {
+    width = self.width,
+    height = self.height,
+    tiles = table.concat(self.tiles),
+    rooms = self.rooms,
+    stairsX = self.stairsX, stairsY = self.stairsY,
+    startX = self.startX, startY = self.startY,
+  }
+end
+
+function Map.fromData(snapshot)
+  local map = setmetatable({}, Map)
+  map.width = snapshot.width
+  map.height = snapshot.height
+  map.tiles = {}
+  for i = 1, #snapshot.tiles do
+    map.tiles[i] = snapshot.tiles:sub(i, i)
+  end
+  map.rooms = snapshot.rooms
+  map.stairsX, map.stairsY = snapshot.stairsX, snapshot.stairsY
+  map.startX, map.startY = snapshot.startX, snapshot.startY
+  return map
+end
+
+return Map