Hokkaido Official Tourism Site HOKKAIDO LOVE!

Witness the dramatic steam and vibrant sulfur crystals of an active volcano.

Mt. Io, also known as Atosanupuri, is an active volcano and the source of the healing waters of Kawayu Onsen. Here, the earth breathes through countless vents, sending thick white steam into the sky and filling the air with the earthy scent of sulfur. It is one of the few places where you can stand within arm’s reach of volcanic activity and feel nature’s energy firsthand.

In the Ainu language, Atosanupuri means “naked mountain,” reflecting its stark appearance. Once a center for sulfur mining, the mountain’s rugged brown slopes remain largely untouched by greenery, creating an otherworldly atmosphere. As you walk the grounds, you can hear the deep rumble of steam rising from the earth, a reminder of its living presence.

The experience at Mt. Io is immersive. You can feel warmth radiating from the ground and the soft touch of drifting steam on your skin. Bright yellow sulfur crystals coat the rocks, creating a vivid contrast against the dark volcanic soil.

At the foot of the mountain, a different beauty appears. From June to July, colonies of Ezo Isotsutsuji (marsh tea) bloom, covering the area in delicate white flowers that contrast with the rugged terrain.

The Tsutsugahara Nature Trail connects Kawayu Onsen to Mt. Io, and guided tours offer a chance to explore while learning about the area’s geology and ecosystem.