Natsuzawa Kousen is a mountain lodge with hot springs located at an elevation of 2,060 meters within a primeval Momi (Japanese fir) forest in Chino City, Nagano Prefecture. It serves as a base for climbing Mt. Iō (2,760m), Mt. Tengu (2,646m), and Mt. Aka (2,899m) in the Yatsugatake mountain range, and is popular among hikers. Despite being relatively accessible at about 30 minutes' walk from the Sakuradaira trailhead, it's a rare mountain lodge with hot springs at over 2,000 meters elevation.

The hot spring is classified as a weakly acidic, hypotonic, cold mineral spring with a pH of 4.53 and a source temperature of only 5.6°C. It contains 92.2mg/kg of metasilicic acid, known for skin-beautifying properties, and 33mg/kg of free carbon dioxide. The water is heated for bathing and circulated/filtered, with occasional chlorine treatment. Separate men's and women's indoor baths are available, with amenities including shampoo, conditioner, and body soap.

Accommodation consists of 7 private Japanese-style rooms ranging from 5.5 to 10 tatami mats, with a capacity of approximately 30 guests. Currently, private rooms are available without additional charge. Electricity is generated by hydropower, limiting use of devices like hairdryers, but Free Wi-Fi and credit card payments are supported. Flush toilets are available, with facilities designed for comfort.

Meals are hearty and popular with climbers. Check-in is from 12:00-16:00, check-out at 8:00. Free shuttle service is available from JR Chino Station for overnight guests (reservation required). Operating year-round, it's a valuable high-altitude hot spring lodge accessible even in winter, highly regarded by mountaineering enthusiasts. Day-use bathing is available for 1,000 yen (tax included), including a commemorative towel with the Natsuzawa Kousen name.