I swear I've seen a thread like this before.
I've explored some abandoned buildings as well, from abandoned houses to abandoned factories. The abandoned houses are quite creepy, me and my friend once ventured into this house that seemed to be stuck in the 80's and a lot of the furniture etc was still in perfect condition. Was pretty dark and creepy downstairs, upstairs we didn't find much except and old kids room, and an old monopoly board, sadly a few years later someone thought it was funny to burn the house down.
Old factory wise me and my friends use to venture inside one that was made into a skate park by some kids, it was pretty cool to see, although a lot of the factory had been looted by thieves. It wasn't the most stable of places either, as this factory was in a town as well it was heavily smashed up by kids.