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. North of the Mt Kimpo, in Tamana, is a spring called Oda no Maru no Ike (尾田の丸池), which used to be a popular swimming spot for the youngsters until their raucousness ruined it all for everyone, as you can see from the sign. There is a foot bath, though, and probably if you’re super quiet, you can swim in the pond. It is connected, springwise, with Kusamakura Onsen, which deserves its own post, so I’ll write about it later. Kakutaxi has more photos and info: https://tinyurl.com/vwzseypu