Got a hole in the wall of our spare room it seems to align with the chimney stack which also has ventilation holes in the attic...3 of them. I can't feel a breeze from it, we live in a radon area so there are breeze blocks through out the property but none upstairs at this height. It's about 6" x 6" wide and looks like a chimney hole. As it has holes going up and down with a ledge underneath as in the photo below. It has been filled in with cardboard then wall papered over.
What am I meant to do with it? It's about 3 foot off the ground never seen anything like it in my life