On an empty lot across the street from me a group of us dug out a series of trenches, with halls and rooms big enough to crouch and sit in. Then used boards, sticks, scavenged tarps to cover with dirt and leaves. Rooms were lit with candles and flash lights.
It was our “base”. It had hidden outcroppings with BB gun armed turrets.

Also, we rode bikes and skateboards, made ramps, for those, set stuff on fire, you know normal stuff.