Hakone Kowakien Onsen Park
While Kowakien has a traditional onsen (Japanese hot spring baths) they also have a kind of onsen theme park! They mix various ingredients into the hot spring water, like green tea, sake, wine, coffee (real coffee, from a large brewer just next to it!) and fruit flavours. They also have a couple of slides, water features and a float tank which is pretty cool (but its very high alkaline or salt something so you can’t stay in there too long!).
