The waters of the onsen are about 50 degrees celsius. It is not possible to bathe with the monkeys, though about 300-400 meters downstream from the onsen for monkeys there is a rotemburo for humans (there are quite a few rotemburo in the Yamanouchi-machi area).
This rotemburo is part of the Korakukan Ryokan (tel: 0269-33-4376) which is an old but excellent wooden ryokan with steep narrow staircases and creaking floorboards.