Iwaobetsu Onsen Sandan-no-Yu is a wild hot spring located in the deep primeval forest of the Shiretoko Peninsula, a UNESCO World Natural Heritage site, at the trailhead of Mt. Rausu (elevation 1,660 meters). Located next to the secluded inn 'Chino Hate,' it is nationally known as a free, 24-hour mixed outdoor bath. Sandan-no-Yu, meaning 'Three-Tiered Bath,' features three pools arranged in a stepped formation. The upper pool has the highest temperature (approximately 35-46°C), with temperatures decreasing toward the lower pools (approximately 30-35°C). While temperatures fluctuate with seasons and weather, the source temperature is a hot 62.4°C. Surrounded by Shiretoko's primeval forest, this secluded hot spring has no changing rooms or enclosures - it is a completely rustic outdoor bath in nature. Though mixed bathing, swimsuits or bathing wear are allowed. Access is relatively easy at about 2-3 minutes walk from the parking lot, making it popular with both hikers and tourists. Nearby is the women-only 'Takimi-no-Yu' where you can bathe while viewing a small waterfall. However, access roads close in winter, so the hot spring is only open from late April to late October.