This is a moderate-sized outpost, complete with a prison cell and a four-story tower. It has hinges that allow you to open it, producing a courtyard or, if opened all the way, a long fortified wall with the tower up front.
This is my first custom LEGO creation. I've had LEGOs for 15 years or so, but never really spent the time to plan out an actual reasonable creation. The images were created using MLcad.