I decided to task while in Berlin. While there I decided to perform this task because there are so many insane buildings. I decided on the Spandau Citadel because we were visiting it and it was... a castle. Does that not spell awesome?
This castle isn't still in use for its original purpose, but serves instead as a place of inspiration for artists with blocks,
I learned that artists and musicians live there on retreat. These artists rent out areas in the castle and work on reconstruction of the history through their art. This is, of course, helping to bring in the tourist crowd that comes to the city: the government AND artists win. Not too bad.
No one can take photographs of the gallery tho' and a guard threw us out because we didn't have tickets. :'[... however, we did run into a medieval instrument jam session. Supposedly an artist still crafts some instruments as well as making violins and other modern instruments.

So since this is a historic site, I guess I should include some information about it:
It was built sometime in the 14th century, it's not really specified.
The tower is called "Juliusturm" after Julius von Braunschweig-Wolffenbüttel, who served as a keep, to the last place of refuge in the fortress; the battlements were added by Schinkel. The castle served as a dungeon for prisoners, as well as a lookout because it is located on the intersection of the Havel and Spree rivers, so there's a moat around the castle to keep people in, or keep people out. Anyone coming in or going out of Berlin via the water would be spotted by the watchers at the Citadel.
It was fortified sometime in the 1500's by the Elector, who wanted to look after his estate and Berlin. The plans were made by Francesco Chiaramella de Gandino, and the first construction supervisor was Christoph Römer before Gandino took over. The building was completed in 1594 under Count Rochus zu Lynar.
The central structure of the citadel is a square pattern, with four pointed bastions known as "König", "Kronprinz", "Brandenburg" and "Königin" at the corners (clockwise from the entrance).

Also, for anyone who's ever watched "I was 19", which is a German film made in 1968, it was never filmed in the Citadel, because it was made in East Berlin while the Citadel is part of West Berlin: the Berlin Wall forced the directors to produce a partial copy in order to shoot a scene. :]