The Imperial Japanese Navy Fengshan Wireless Communications Station atlasobscura.com

It was initially built by the Japanese Navy between 1917 and 1919 as one of three large-scale wireless telecommunication centers in the Pacific.
It remained under Japanese control until the end of World War II, when Taiwan was reunited with the Republic of China.
During the Japanese use of the facilities, this building housed the main communication equipment, and was designated as the First Sending Telecommunication Station.
During the Fengshan Guest House period, prisoners allegedly called it “the cave,” in reference to its size and the way it was built into a hill.
In 2011, the former communications station and detention center was opened to the public.