JDF JapanDefenseFocus No.91




Japan has a number of limestone caverns across the country which are formed when limestone was eroded by surface and underground water. Located in Iwate Prefecture, Ryusendo is one of Japan's three largest limestone caverns.

The known length of this cavern formed over many ages is 3,600 meters and there are eight confirmed underground lakes inside. There are also five species of bats that live inside the caverns and their rather strange natural surroundings that appear to be frozen in time. The cavern and these bat species are both designated as natural monuments and protected animals by the Government of Japan.

The cavern was closed in the autumn of 2016 due to torrential rainfall caused by typhoons, but it reopened to visitors in March 2017. The part open to the public includes 700 meters of caves and three underground lakes.

The third underground lake located at the end of the tour area is 98 meters deep and its waters have an extremely high clarity.The lake water is a true blue beyond one’s wildest imagination. Back in 1985, the mystic water of Ryusendo’s underground lakes was selected as one of Japan’s top 100 waters.

Ryusendo is located in Iwate Prefecture, which is home to JGSDF Camp Iwate and JASDF Yamada Sub-base. These bases, located close to the Iwatesan Exercise Area, employ approx. 1,500 personnel who strive to train day and night.

JASDF Yamada Sub-base is under JASDF Misawa Air Base and is the home base for the 37th Aircraft Control and Warning Squadron.

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