Otari Onsen Yamada Ryokan is a historic hot spring inn with over 450 years of history, located at an elevation of 850 meters within Myoko-Togakushi Renzan National Park in Otari Village, Kitaazumi District, Nagano Prefecture. The spring was reportedly discovered in 1555 by a retainer of Takeda Shingen during the Kawanakajima Battle. This solitary inn preserves six wooden buildings from different eras - Edo, Meiji, Taisho, and Heisei periods - all designated as National Registered Tangible Cultural Properties.

The hot spring features two natural sources (Motoyu and Shinyu) that flow directly from behind the inn at a rate of 150 liters per minute. The water is a sodium bicarbonate spring with a source temperature of around 44°C, characterized by slightly brownish-tinted water with a soft, smooth texture. The baths are 100% natural flow-through (kakenagashi) with no heating, cooling, or circulation, and contain radon. The water is believed to be beneficial for liver disease, diabetes, skin conditions, and burns.

There are two bathing areas: the main bath (Motoyu) and a scenic observation bath (Sotoyu) with stunning mountain views. Both are separated by gender and offer beautiful views while bathing. The inn comprises 28 rooms across multiple buildings representing different architectural periods, including the Edo-period main building, renovated Meiji wing, Taisho wing, and modern Heisei annex. Four rooms have private baths and toilets, four have toilets, and twenty are standard rooms.

The inn maintains the traditional toji (therapeutic bathing) culture, offering self-catering options for long-term stays. Meals feature local mountain ingredients prepared in a simple, traditional countryside style. The inn is also close to the Mt. Amedaki trailhead, making it popular with hikers. As a member of the Japan Secret Hot Springs Preservation Association, Yamada Ryokan continues to preserve the atmosphere and traditions of a traditional therapeutic hot spring resort.