While my stay in Karuizawa, somtimes I go to Tombo-no-yu, a communal bathhouse at Hoshinoya area with my wife and son. But we do not take bath so often, but rather spend 1 or 2 hours around the bathhouse. There are some hills with a little path on a grass field and there is a cafe next to the bathhouse.
For anyone interested in Tombo-no-yu, although inside is not so spacious, hot spring water is good. As many other popular sites in Karuizawa, I would not recommend going there during weekends in summer and golden week in May. Much too crowded during the holidays, though it would not be so bad as a rush-hour train in Tokyo. I like going there during weekdays. The fee for bath is a bit pricy — 1200yen for adult, 700yen for children. It’s open: 10:00 a.m. – 11:00 p.m. (Last admission 10:00 p.m.) TEL: 0267-44-3580.