Zao Onsen & the Okama Crater

In winter, Mt. Zao is the realm of the frozen “snow monsters.” But come summer, the same mountain is a cool green escape from the lowland heat — and its single most jaw-dropping sight is a lake the color of a marble.

Why It’s Interesting

The Okama (“the cauldron”) is a near-perfect round crater lake cupped between three peaks, its mineral water glowing a vivid, shifting emerald to teal that looks almost artificial. A short walk or drive from the summit road brings you to the overlook. Below it, Zao Onsen is one of Tohoku’s oldest hot-spring villages, its streets steaming with milky, sour sulfur water perfect for an after-hike soak. Up high the air stays cool even in August, which is half the appeal.

Best Time to Visit

The crater and high trails open roughly late spring through autumn; the lake is greenest on a clear, calm day — fog can swallow it entirely.

Getting There

Bus from Yamagata Station to Zao Onsen, then the ropeway or the Zao Echo Line toll road up toward the Katta summit for the short walk to the Okama.