Noboribetsu Onsen — Hell Valley Hot Springs

Noboribetsu Onsen (登別温泉) is Hokkaido's premier hot spring resort, fed by Jigokudani ('Hell Valley' — 地獄谷), a volcanic crater spewing steam, sulfurous gas, and boiling water from dozens of vents. The valley's barren, yellow-gray landscape dotted with steaming fumaroles resembles a hellscape (hence the name), and the minerals from this volcanic activity create nine different types of hot spring water — the most diverse in Japan.

The resort town's ryokan and public baths draw directly from these sources, offering sulfur, iron, acidic, and saline baths. Walking through Jigokudani on wooden boardwalks while steam billows around you feels otherworldly. The sulfur smell is intense but the sight of the volcanic landscape is unforgettable.