• Kyodo

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The longest limestone cave in Japan is nearly twice as long as previously thought, according to a spelunkers’ group from Chiba.

The Association for Cave Exploration said it recently mapped Akkado cave in Iwate Prefecture as being 23.7 km long — so far. The nonprofit organization will present its findings to the Japan Association of Groundwater Hydrology at a meeting May 20 at the University of Tokyo.

Mazelike Akkado features an underground lake measuring 2 km along its north-south axis, 500 meters on its east-west axis and at least 140 meters deep, the explorers said.

The group, which measured the cave as being 12.7 km long in 1997, hit the 23.7-km mark in March.

Japan’s second-longest limestone cave is Oyama Suikyodo on Okinoerabu Island in Okinawa with a length of 10 km.