The Tunnels of the underground Japanese Navy Headquarters, Okinawa.
http://kaigungou.ocvb.or.jp/english/
https://japancheapo.com/place/kaigungo-navy-underground/#:~:text=The%20Former%20Japanese%20Navy%20Underground%20Headquarters%2C%20or%20%E2%80%98Kaigungo%E2%80%99%2C,the%20Japanese%20Navy%2C%20and%20an%20underground%20air-raid%20shelter
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