Ok this is weird. Went through that thread and someone mentioned tunnels under schools and I suddenly had a very vivid memory of my friends and I discovering a strange tunnel under my junior high school gym growing up. We had two gyms, actually, one right next to the other (girls locker room and basketball court on one side and the same for te boys on the other). To get into either gym you’d walk down a narrow hallway and in both hallways there was a trap door that always creeped us out. They were usually locked but one day we noticed one wasn’t and my friends and I climbed down the fixed ladder a good eight feet down to the bottom. We assumed they would be some kind of underground utility closet or something but we brought a flashlight and looked in either direction and didn’t see any equipment of any kind and literally could not see the end of the tunnel in either direction. It scared the shit out of us and we climbed back up as fast as we could go. Word spread about the tunnel (my fault probably I was a big talker even back then) and other students started venturing down to get a look. This was kept from the staff until one day someone either forgot to close it, or left it open on purpose—we never found out who did it because one day someone came out of one of the gyms after PE and fell down it and messed their leg up pretty bad. They were padlocked after that and we never saw it open again after that. We always guessed it was some cold war era bomb shelter or something but it was such a narrow space that never really made sense to me. Shit. Now I’m wondering…