Tokyo doesn't have natural onsen within the city itself (Oedo-Onsen in Odaiba uses drilled hot spring water), but within 2 hours there are some of Japan's most celebrated hot spring areas. Here are the best options by distance.
Hakone (90 min from Shinjuku)
Japan's most accessible mountain onsen destination. Strong sulfur springs with Mt. Fuji views. Day-use options: Tenzan Tohji-kyo (outdoor baths in forest, ¥1,300) · Hakone Kowakien Yunessun (spa-park hybrid, ¥2,500) · Gora Kadan (high-end day-use with reservation). For the full experience: book a ryokan overnight with private rotenburo. Access: Romancecar from Shinjuku (85 min, ¥2,470).
Kusatsu Onsen (2 hrs from Shinjuku)
One of Japan's top three onsen towns — famous for its yumomi tradition where large wooden paddles cool the impossibly hot spring water while women sing. The flow of Yubatake (hot spring field) in the town center is extraordinary. Day-use options: Netsu-no-yu public bath (¥600, 45-min timed entry); multiple other public baths free or ¥500. Strong acidic water — therapeutic but can sting cuts. Access: Shinkansen to Takasaki + bus (¥4,200 total, JR Pass partially covers).
Nikko Yumoto Onsen (2 hrs from Ueno)
High-altitude onsen at 1,478m elevation in Nikko National Park. Combined with Nikko's Toshogu Shrine and Kegon Falls for a full day. Day-use options: Yumoto Onsen Yoshimoto (¥550). Sulfur-white water. Access: Tobu Nikko Line + bus.
Atami Onsen (1 hr from Tokyo)
Coastal onsen town on Ito Peninsula — ocean views from some outdoor baths, multiple public bathhouses. Day-use: Multiple soto-yu (public baths) in town for ¥200–¥500. Seafood lunch before or after. Access: Shinkansen to Atami (50 min from Tokyo, ¥3,640). Or JR Tokaido line (slower, covered by JR Pass).
Ikaho Onsen (2 hrs from Shinjuku)
Famous for brown iron-rich "golden water" onsen — distinctive rusty color believed to have therapeutic properties. Stone staircase shopping street is the main aesthetic draw. Day-use: Ishidanyu public bath (¥700). Access: Shinkansen to Takasaki + bus.
Oedo-Onsen Monogatari Aqua Garden (Odaiba, Tokyo)
Not a natural hot spring town, but a well-designed urban onsen experience in Odaiba — drilled natural hot spring water (sodium chloride, 44°C), outdoor foot bath garden, yukata provided, festival food stalls. Good for a half-day when staying in Tokyo. Admission ¥2,948 (online advance price). Access: Yurikamome Line to Telecom Center.