First, lock the core in a solid rectangle with three‑tile‑thick walls—no gaps. Then add a concentric ring of walls that forms a spiral corridor. Each turn should lead to a dead‑end that loops back toward the center, so enemies get stuck in a loop. Use diagonal walls inside the ring to create false paths; these look like real routes but end in a 1‑tile choke point that you can fill with a turret. Keep the entrance a single gate that funnels traffic into a five‑tile‑wide hallway, then into the central hub. Finally, place a 4‑tile buffer zone between the outer wall and the core so you always have room to react. That way the fortress is bullet‑proof, the maze is confusing, and the defense stays tight.

Add a pressure plate in a secondary corridor that’s a tile away from the main spiral loop. When a creep steps on it, it triggers a hidden door that slides into place along a 3‑tile wall. That door should be covered with a paint‑matching panel so it’s invisible unless you’re watching the trigger. Make sure the secret room is a 2‑by‑2 square with a quick exit back to the core—no room for the enemy to get stuck forever. Keep the trap on a wall that’s still at least 3 tiles thick so even if they open the door, the rest of the fortress stays solid. This gives you that “surprise” element while not compromising structural integrity.