1. Buy a new bed and keep the MDF and polystyrene packaging it came with.
2. Cut up MDF into squares and glue on textured wallpaper.
3. Carve up the polystyrene packing.
4. Attach polystyrene with PVA to create passages, room corners and interesting cavern features.
5. Get painting! Acrylic paint!
7. Water down a darker colour.
8. Get painting!
9. Make a Walled Keep with anything left over. ;)
10. Ready for gaming!
11. Or just play in the driveway!