Lake Suwa

Suwa sits at about 760 metres in a basin on the Fossa Magna, the tectonic trough that crosses central Honshu, and it is fed by hot springs - the town of Kamisuwa has public baths and a geyser on the shore. The phenomenon it is known for is the omiwatari: in a hard freeze the ice sheet expands and contracts with day and night temperatures until it fractures and the broken edges push up into a ridge running across the lake, sometimes a metre high. Shinto priests at Suwa Taisha have recorded its appearance since the fifteenth century, which makes the record one of the longest continuous climate observations anywhere; it now forms far less often than it did, and several recent decades have passed with almost none. The lakeside is otherwise a ring road with onsen, a summer fireworks festival among the largest in the country, and views to the Yatsugatake range.

What you actually see

• The omiwatari - a pressure ridge pushed up across the ice in a hard freeze.
• A six-century record - shrine priests logging its appearance since the 1400s.
• Hot springs on the shore - public baths and a geyser at Kamisuwa.
• A summer fireworks festival - among the largest displays in Japan.

When to go

January and February for a chance of the ice ridge; August for fireworks. A day.

Honest expectations

The omiwatari now forms rarely and cannot be planned for. The lakeshore is developed and the ring road is not scenic in most sections. Water quality has been a long-standing problem. The fireworks festival brings extreme crowding and booked-out accommodation.

Nearby

Suwa Taisha's four shrines are around the lake; Matsumoto is north.