This lovely Shizuoka onsen town has a number of hotels, minshuku, and spas sprinkled about, but you'll probably want to check out the very unique matchaburo (green tea bath) at the Tsuribashi-sou (つりばし荘). Three baths are housed in a wonderfully aromatic enclosure made of cypress wood that overlooks the river. You reserve a bathing time in advance and someone from the Tsuribashi-sou will prepare the matcha for you just prior to your getting in. The baths are small goemonburo but the scent of green tea steam is an experience everyone should enjoy. For added ambiance be sure to order the tea service which can await you when you get out, or an icy cold bottle of sake served in beautiful bamboo shot glasses.
Getting here is easiest with a car, and you'll have fun with the corkscrew highway that goes around in two 360 degree turns like a spiral staircase. Once here, be sure to plan on stopping across the river at the Cave bath, where you can soak either in the faux grotto or in several nice pools that overlook the river.