Akaigawa Caldera

The Akaigawa Caldera is a volcanic depression across the mountainous terrain of Hokkaido, displaying distinct rocky outcrops of andesite, dacite, and rhyolite at around 725 meters in elevation. Steep slopes and natural hot springs characterize the geological landscape of this formation.

The caldera formed through volcanic activity roughly 1.7 to 1.3 million years ago during the Pleistocene period. This ancient volcanism shaped the region's geological character and created the conditions for the thermal springs found here.

The natural hot springs in the caldera offer traditional Japanese onsen experiences where visitors soak in mineral-rich waters that are warmed by the earth's heat.

A bathhouse here features large windows facing a massive rock wall, allowing visitors to observe geological formations while soaking. Visiting early in the day or later in the afternoon tends to be less crowded than midday hours.

The water in the bathing areas maintains a constant temperature of around 50 degrees Celsius, heated entirely by natural geothermal processes beneath the ground. This active geothermal heating system is what draws both locals and visitors seeking this particular type of thermal experience.