diff --git a/src/game_state.h b/src/game_state.h
index edfca31..e9e534f 100644
--- a/src/game_state.h
+++ b/src/game_state.h
@@ -1,11 +1,13 @@
 #pragma once
+
 /* This houses the state of an actual, running game; your player, the
-   other players, the world map, buildings. TODO: move some stuff to
-   separate files. */
+   other players, the world map, buildings. */
 
 #include <glib-2.0/glib.h>
 #include <SDL3/SDL.h>
 
+#include "world.h"
+
 typedef struct Player
 {
   unsigned int id;
@@ -18,41 +20,10 @@ typedef struct Player
   gboolean is_alive : 1, is_human : 1;
 } Player;
 
-typedef enum TerrainType
-  {
-    TERRAIN_WATER,
-    TERRAIN_FLAT,
-    TERRAIN_HILL,
-    TERRAIN_MOUNTAIN
-  } TerrainType;
-
-typedef struct MapTile
-{
-  unsigned int x, y;
-  unsigned int owner_id;
-  TerrainType terrain_type;
-
-  gboolean is_defended : 1, is_radiated : 1;
-} MapTile;
-
-typedef struct Building
-{
-  MapTile *parent_tile;
-  unsigned int level;
-} Building;
-
-typedef struct World
-{
-  GArray *tiles;
-  GArray *buildings;
-  unsigned int width, height;
-} World;
-
 typedef struct GameState
 {
-  World world;
-
-  GList *players;
+  World *world;
+  GArray *players;
   Player *me;
 } GameState;
 
diff --git a/src/world.c b/src/world.c
new file mode 100644
index 0000000..fae69fe
--- /dev/null
+++ b/src/world.c
@@ -0,0 +1,2 @@
+#include "world.h"
+
diff --git a/src/world.h b/src/world.h
new file mode 100644
index 0000000..80ee669
--- /dev/null
+++ b/src/world.h
@@ -0,0 +1,39 @@
+#pragma once
+
+#include <glib-2.0/glib.h>
+
+typedef enum TerrainType
+  {
+    TERRAIN_WATER,
+    TERRAIN_FLAT,
+    TERRAIN_HILL,
+    TERRAIN_MOUNTAIN
+  } TerrainType;
+
+typedef struct MapTile
+{
+  unsigned int x, y;
+  unsigned int owner_id;
+  TerrainType terrain_type;
+
+  gboolean is_defended : 1, is_radiated : 1;
+} MapTile;
+
+typedef struct Building
+{
+  MapTile *parent_tile;
+  unsigned int level;
+
+  unsigned int (*at_what_cost) (Building *self, World *world);
+} Building;
+
+typedef struct World
+{
+  unsigned int width, height;
+  GArray *tiles;
+  GArray *buildings;
+} World;
+
+World *World_new (unsigned int width, unsigned int height);
+void World_tick (World *self);
+void World_render (World *self, GfxContext *gfx_context);