One of the day use hot springs in Yufuin. This is a mixed men and women bath, however there were no women in the bath when I went.
It is a long walk from the train station so time your bath accordingly. Great place from the metal pillar for paying the bathing fee to the wooden baths. The outdoor bath is pretty much open to view from the adjoining small pond so be careful about exposing it all--or not.

General note about mixed baths: Men, please do not make this place unfriendly to women visitors--be considerate of your actions.

Interesting locals only neighborhood bath on the way here was interesting to see. This one was not open to the public and the many, many signs made sure you know that and that photography was not permitted.