Sukayu Onsen Sennin Buro

The sennin-buro ("thousand-person bath") at Sukayu is a vast, cavernous hall built entirely from hiba cypress, a wood with natural antibacterial properties and a warm, resinous scent. The hall has been here for about 300 years, and stepping inside still feels like entering another era: low light filtering through the steam, the smell of sulfur, the sound of water. It is a mixed bath (konyoku), and a rental yuami-gi wrap is available for those who want one. Women have two dedicated women-only periods each day (8-9am and 8-9pm). The water is highly acidic and sulfurous, so keep metal jewelry off, as the reviews note it tarnishes quickly.