Okinawa was a spot of major strategic importance in WWII -- due to its location you could bomb pretty much everything important from there without too much trouble. No wonder that vicious battles have been fought here with casualties like 100 thousand Japanese people and 12.5 thousand American soldiers. The Americans methodically scorched the whole island*, so the number of civilian casualties is extremely high.
This is an underground bunker, that used to be a Japanese Navy Headquarters. Quite spooky..
* Well, not that they had much of a choice. War's tough.
