Yunomine Onsen is a quiet, peaceful onsen town whose jewel is the humble Tsubo Yu, a small, extremely hot spring where pilgrims along the Kumano Kodo path would stop to purify themselves before their final approach into Hongu Taisha Shrine. It's a unique bath which is open to the public on a first-come, first-served, reservation system. You reserve a 30 minute bathing time and then use the bath when your turn arrives. Be careful not to scald yourself...at 90 degrees Centigrade, this water is HOT!
As with many of the area's onsen, Yunomine Onsen is best reached with a rental car if one wants flexibility -- otherwise you'll use the bus. It's delightful, peaceful place. Unlike some onsen waters, those here at Yunomine are potable, meaning you can find onsen-made coffee, tea, onsen-boiled eggs (known as onsen tamago), or the Do-It-Yourselfers can bring their own eggs or vegetables and boil them in the public cooking area. Yum!