This is a weird little place. Mad Mark was supposedly a crazy guy who would tell his strange ideas to folks in this castle, which is complete with a spiral staircase. The interior has many bizarre paintings (like this one) and it gets regularly painted in weird colors. It's location is off of a path overlooking a cliff on the extreme tip of the bulb just south of the gate area.
Castles, Artwork - Land Art/Geoglyphs