A concept for a fort I had, inspired by the conversation in "Kingdom of Heaven", between Balian and the King. They spoke about a fortification design in the shape of "a star, that way no part of the fortress may be approached, without being exposed to fire from another part".
Eventually it turned into this full-blown "level design" with rotational symmetry (Each of the six points are identical). Complete with interiors (unfurnished), so there are actual walls inside, and not just the outer "shell" you see.
Feel free to use it in your own game/level designs/mods, as it's perfect for teams or single players. Just throw me a mention, and let me know if you've used it.