William Tatsudayama was created by tectonic uplift, apparent when hiking: its clay composition is so slippery gravel must be poured on paths. Mt Kimpo, conversely, is a dormant volcano (yes! it could erupt again! imagine that!) composed of granite; the stone used to create the castle walls was quarried there, leaving a large pit called Ishigamiyama kōen (石神山公園, photo below) which is filled with water but completely fenced. Even I wouldn't swim there: too dangerous, but the views of the city are nice. It's a scenic, short hike from the street car.