Imagine this: You find a mountain, and discover it's covered by a dwarven fortress. You climb to the top and find a very deep hole. You jump down, and at the bottom is a massive cavern full of ancient relics and statues. And at the far end, you see a wall, and a gate with large blue torches on either side. You walk in, and there you see the real fortress, hidden from all but the dwarves that built it.