Zao Onsen Summer: The Hot Springs Town That Transforms Without Snow

Zao Onsen is most famous for its winter ice monsters (juhyo) — the ice-covered trees on the Zao ski slopes that form when supercooled fog freezes on the branches of fir trees, creating shapes that look less like trees and more like creatures emerging from snow. The photographs circulate. The winter crowds come.

What fewer people know is that Zao Onsen in summer is a different and in some ways more rewarding destination. The crowds are smaller. The sulphur baths are unchanged. The landscape above the town — volcanic ridgeline, crater lake, alpine plateau — is accessible without skis. This is a guide to Zao Onsen outside of ski season.

The Hot Springs

Zao's hot springs have been in use since the 7th century. The water is strongly acidic (pH 1.2–1.8) — among the most acidic of any hot spring in Japan — with a distinctive whitish-green tint from the sulphur content. The feeling on skin after bathing is of a light polishing. The water has a long reputation for treating skin conditions.

The Dai-rotenburo (大露天風呂) is Zao Onsen's signature communal bath — an outdoor pool of approximately 200 square metres, open from late April to late November, fed directly from the volcanic spring. Mixed bathing (konyoku) with swimwear permitted. In summer, the surrounding forest is full and green above the steaming bath. In autumn, the hillside colour is extraordinary.

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Individual ryokan baths throughout the town offer indoor options year-round. The town's shared bathhouse network (four separate bathhouses) allows day visitors to bathe for ¥200–300 per session.

Summer Activities

Zao Echo Line

The Zao Echo Line is a toll road that crosses the volcanic massif at approximately 1,400 metres, connecting Yamagata to Miyagi. In summer, it passes through alpine meadows with views over the Sea of Japan and the Pacific simultaneously on clear days. The road is closed in winter (November–April) and spectacular at the beginning and end of autumn colour season (October).

Okama Crater Lake

The Okama crater lake sits at 1,460 metres, accessible from the Zao Echo Line viewpoint. The lake's colour — an intensely vivid green-blue from the volcanic minerals — changes with light conditions and from season to season. The viewing platform is 15 minutes on foot from the nearest parking area. In clear summer weather, the lake is at its most photogenic in the morning.

Hiking

Summer hiking routes on Zao mountain include the traverse from the ropeway summit to Okama Lake (approximately 3 hours), the Jizo ridge walk with views north and south, and the Kumano-dake summit (1,840 metres) above the ski area. The ropeway operates year-round and provides access to the upper trails without the ascent.

Getting There and Where to Stay

From Yamagata Station by bus: 40 minutes (Zao Onsen Bus Terminal). From Tokyo by shinkansen to Yamagata, then bus: approximately 3 hours total. The bus is the standard approach; car rental from Yamagata station is useful for the Echo Line drive.

Zao has approximately 40 ryokan and hotels in the onsen village, ranging from large resort properties to small family-run ryokan. Summer rates are 20–30% lower than winter peak. The onsen experience is unchanged. Takamiya, Zuihokaku, and Zao Onsen hotel are consistently well-regarded across seasons.