If you have much time in Japan and want to try the hot spring bath then you can find them around Japan. They are abundant as it is in the favor of the location of the country where the volcanic activity is active. Other nationalities just normally have a shower but in Japan, they do take bath as a regular routine and they also can get them in the onsen. Onsen is the Japanese term for the hot spring and you can find the signs that point to them.
They could be easy to find but you can also ask for locations.
In Japan, it is normal to have some baths in the onsen and not just for one person but it could be for the family, for acquaintances and others. They can make it as their gathering place and enjoy the bath together. Onsens could be indoor or outdoor. The second one is more common and it comes with different shapes and also styles.
The indoor ones are usually built by hotels or inns or other places to stay.
It is great that while traveling you can choose to stay in a place where you can also take a bath and relax. With all the activities you have done, it is due to have the time to relax.
If you are the type that is not used to being naked with people then bring a good big towel to cover your body. But you should remove it when you will be in the water.
These baths could be managed by the municipality it is located or by a private owner.