Washizawa Wind Cave (鷲沢風穴) 鷲沢風穴
A horizontal ceiling, unique in Japan among limestone caves; 400 yen, helmet included.
The cave takes its name from the Washizawa area, in Hamana Ward, Hamamatsu. It is one of the ‘100 natural sites of new Hamamatsu’ (新浜松の自然100選), a municipal list. Inside there is also a pond dedicated to the water god.
Shizuoka
https://theanimetrip.com/luoghi/grotta-del-vento-di-washizawa