noun
limestone cave; limestone cavern
A natural underground cavity formed in limestone, often featuring stalactites and stalagmites.
秋芳洞は日本最大級の鍾乳洞です。
Akiyoshidō is one of the largest limestone caves in Japan.
鍾乳洞の中は夏でもひんやりして
It's cool inside the limestone cave even in summer.