Katsuragi Onsen Happu no Yu
This hot spring resort located at the base of Mount Koya allows you to soak in four varieties of source waters. One in particular is dubbed “fossil seawater”: water from the ocean that tens of thousands of years have turned into brownish-red hot-spring water with a salt concentration among the highest of any in Japan. You can enjoy the hot spring for the day, or treat yourself to a night in the guest rooms, some of which have their own private open-air bath.
702 Saya, Katsuragi-cho, Ito-gun, Wakayama Prefecture
5 min. walk from JR Kaseda Station
Lodging starts at 16,500 yen per night (includes dinner and breakfast); 1,000 yen for the hot spring for day visitors
Check-in: 15:00; check-out: 10:00