Image by Miguel Michán - www.miguelmichan.com Getty Images

This stunning outdoor onsen offers four large rock pools cascading beside Tone-gawa and shaded by a lush forest with meandering paths, wooden huts, and folk and religious statues. All pools are mixed, except one that's for women only. Modesty towels are available (¥100) but seem to be used only by women. Buses run here hourly from Minakami Station (¥2900, 40 minutes).