This is a tansan-sen, or carbon dioxide hot spring, in Kawachinagano City on the southern edge of Osaka Prefecture. It seems like its existence isn't well known.

This one's somewhat gloomy and humid. Rumor has it that snakes appear. A hot spring for the courageous!

This kind of open-air hot spring is rarely seen: a dip in a polymer pool. The temperature is moderate and, oddly enough, you're surrounded by wilderness.

It seems this one's on the far side of a private home in Sukagawa City in central Fukushima. He asked permission first.

This is just overflow from a hot spring connected to a private house. Yet the water flows out of the wall at a temperature of 50°C (122°F)! Gunji had to bring his own kiddie pool to take a dip.