Lake Haruna, Volcanic crater lake in Takasaki, Gunma Prefecture, Japan

Lake Haruna sits inside the caldera of Mount Haruna at about 1,084 meters (3,557 feet) elevation, creating a small, deep basin surrounded by forested slopes. The water reflects the green hillsides that rise around it, with clear views across the volcanic crater rim.

Lake Haruna occupies a caldera on Mount Haruna whose rim took shape about 42,000 years ago; the basin then held a much larger lake. Eruptions around 31,000 years ago built the lava dome of Haruna Fuji as an island in that water. Debris from later eruptions, including Futatsudake in the Kofun period, gradually filled the basin to its present outline. By the Nara period the lake was sung in the Man'yoshu as Ikaho Marsh.

The lake was long called Ikaho-numa and appears in the Manyoshu, and by the Edo period farmers across the Kanto formed Haruna-ko groups, carrying spring water from Haruna Shrine home in bamboo tubes to pour on their fields for rain. Near the shore stands Minuma Okami Shrine, where red rice is floated on the lake on May 5 for the princess said to have become its dragon deity.

The easiest way to reach this place is by bus from Takasaki or by car from the nearby highway interchange. Roads to the crater can become slippery in bad weather or winter months, so sturdy footwear and careful driving are recommended.

The road leading to the lake has special grooves carved into its surface that produce a melody when vehicles drive over them. This unusual musical feature catches many visitors by surprise as they make their way up to the water.