We found a small hill, that lots of cement a japanese cement, lots of century tree one of them is Jackfruit, there is a lady statue with a seating position there is a flag poll of a japanese.
This reminds of that post a few years ago about the guy who found a mass of concrete on hill. Anyone remember that? Wish I could help you further abacus but with little info you have provided, it's going to be tuff. If your in Japan possible WWII bunker ?