Yunotani Onsen Poribasu-no-yu

A no-frills wild bath (noyu, 野湯) beside a prefectural road in the mountains of Kozagawa, Wakayama. Hot spring water gushes out of the hillside and straight into a stainless steel tub at such a rate that the water turns over completely in under a minute, you're always in fresh, flowing spring water. It's a simple sulfur spring with a clear egg-smell, unmanaged and free. No changing room, no amenities, just the tub, the hillside, and the road going past.