Nasu Onsen — Royal Retreat Hot Springs

Nasu Onsen is a collection of seven hot spring sources scattered across the volcanic slopes of Mount Nasu, a highland resort area that has been a summer retreat for Japanese aristocracy and, since 1926, the imperial family. The imperial villa (Nasu Imperial Villa) occupies 660 hectares of forested land; while the villa itself is closed, the surrounding Nasu Kogen plateau offers public onsen, hiking trails, highland pastures, and cool summer temperatures (10°C cooler than Tokyo).

The seven onsen sources (collectively called Nasu Shichi-yu) vary in water type — sulfur springs (milky white, strong smell), iron springs (rust-colored), and simple alkaline springs (clear, smooth). The most famous is Shikanoyu, the oldest onsen in the Kanto region (discovered 1,380 years ago), with milky sulfur water and rustic wooden bathhouses. The area combines onsen culture with outdoor activities — hiking Mount Nasu (1,915m), visiting dairy farms, and enjoying resort amenities. It is upscale-rustic, nature-focused, and noticeably less commercialized than other major onsen towns.