Why is it called Black Tower Castle?

Black Tower Castle is the home of Timmy and the gang. It is built atop lightless caverns of doom, horror, and despair. It is also one of the most famous castles in the world. So where does its name come from?

Is it a metaphor for the black hearts of its previous owners? Is it a statement of its power and prestige?Nope.Way, way, way back when it was first built, the largest, most visible part of the structure was a black tower. Now, was that the same tower Timmy tossed Katie out? Who can say....