Photo/Illutration Visitors stroll by ice placed inside the Narusawa Ice Cave on Aug. 12 in Narusawa, Yamanashi Prefecture. (Wataru Sekita)

NARUSAWA, Yamanashi Prefecture--The Narusawa Ice Cave, a national natural treasure located here at the foot of Mount Fuji, has proved a popular sanctuary for people trying to escape the continuing summer swelter.

Inside the ice cave, the temperature stays around 2 to 3 degrees, even in mid-summer.

Long lines have formed by people seeking to enjoy the chilliness and cool lighting underground.

The cave was formed when lava from the eruption of Mount Fuji more than 1,100 years ago gradually cooled and contracted, expelling gases from the interior and creating a cavernous void.

In the days before refrigeration, the cave was used as a natural cooling site with ice from frozen Saiko Lake nearby.

At the deepest part of the cave, 21 meters below the surface, ice brought in and piled up last December was lit up in blue this summer, creating a fantastic atmosphere.

Rio Shoji, 10, who visited the cave with her family from Tokyo, said: “It was cold even with a jumper on. It was hot outside, but it was cold inside.”

Her younger sister, Riko, 7, said, “The ice lit up was beautiful.”