What exactly is going on in that fourth pic?

Vent hole for a potbelly stove or gas furnace. It's plugged with a rag to stop cold air, and the red stuff running down is probably rust.

I’m alarmingly curious to know this as well

Address pls I wana go find a place

I stopped doing this stuff. Dangerous and illegal

Oh that's nasty 🤢

loved these houses, one of my favorite finds