Momonoki Onsen Sanwaso is a secluded hot spring inn located in the Ashiyasu area of Minami-Alps City, Yamanashi Prefecture, nestled in a valley along the Midai River. The inn was established in 1988 in an area historically known as 'Momonoki-daira' (Peach Tree Plateau) due to its abundance of wild peach trees. The hot spring was discovered through boring in 1992, reaching a depth of 999.67 meters with an impressive flow rate of 372.4 liters per minute. The water is classified as an alkaline simple hot spring with a pH of 9.59, making it renowned as a 'beauty skin' spring that leaves skin silky smooth. The source water at 42.6 degrees Celsius is delivered to the baths as 100% free-flowing natural spring water with no dilution, heating, or recirculation. The inn is a member of the Association to Preserve Japan's Natural Source Hot Spring Inns. The rustic stone-built open-air bath offers views of the magnificent Southern Alps during the day and a canopy of stars at night. A unique feature of this inn is that all rooms are pet-friendly, allowing guests to enjoy meals, hot springs, and accommodation together with their dogs. Children under junior high school age are not permitted. Day-trip bathing is available for 1,000 yen per adult.