The remote interior of eastern Hokkaido cradles a trio of magnificent caldera lakes within Akan-Mashu National Park — a landscape of crater lakes, volcanoes, steaming earth and deep forest. Lake Akan is famous for its rare spherical marimo algae and a lively onsen town with an Ainu kotan; Lake Mashu is one of the world’s clearest lakes, often wrapped in an ethereal mist; and vast Lake Kussharo offers free lakeside hot springs and sweeping caldera views. Volcanic Mt. Io and the Sunayu sand-baths complete a primeval, otherworldly region.

This guide covers the three lakes, onsen, viewpoints and how to get there.

🗓️ Quick Reference
Location Eastern Hokkaido (Akan-Mashu NP)
Highlights Akan marimo, Mashu mist, Kussharo onsen
Time needed 1–2 days
Good for Lakes, onsen, volcanoes, Ainu culture

Lake Akan

  • A forest-ringed crater lake famous for marimo — rare green algae balls — with a museum and boat tours.
  • The lakeside onsen town has hot-spring inns and the largest Ainu kotan in Hokkaido, with crafts and performances — see our Upopoy guide for more Ainu culture.

Lake Mashu & Lake Kussharo

  • Lake Mashu: astonishingly clear and steep-walled, frequently shrouded in mist — admired from rim viewpoints (no shore access). Hauntingly beautiful.
  • Lake Kussharo: Japan’s largest caldera lake, with free open-air hot springs at the shore (Kotan, Sunayu sand-baths) and a great panorama from Bihoro Pass.
  • Mt. Io (Iozan): a hissing, sulphur-stained volcano you can walk up to, between Mashu and Kussharo.

Onsen & getting around

  • The region is rich in hot springs — lakeside resorts and free natural baths alike.
  • It’s spread out and remote; a rental car is by far the best way to link the lakes and viewpoints.
  • Misty mornings and crisp autumn days are especially atmospheric.

Combine your visit

These lakes pair with the wild east coast:

  • Combine with the Shiretoko Peninsula to the northeast — see our Shiretoko guide .
  • In late winter, add Abashiri drift ice on the coast — see our drift ice guide .

How to get there

  • Fly to Kushiro or Memanbetsu, then drive (~1.5–2 hours) — a rental car is recommended.
  • Lake Akan has bus links and tour access; Mashu/Kussharo are easiest by car.