Hidden room found in my basement! What should I do?

I was following a leak in my basement and tore out some sheet rock, only to discover a 11×3 foot long space I didn’t know was there. The wall on the left is the exterior of the house, and the one on the right is the one adjacent to the basement/cellar interior. The previous landlord had finished the basement and it never crossed my mind that something might be there. If I could somehow open up that wall, I could add 4.5 feet of width to my basement/cellar rec room, and ideally a add a toilet. However, it seems pretty apparent that it is a load-bearing wall. I think these walls basically mirror the width of the stairway above it. It is an old stone masonry wall. This is in a balloon-frame wood 3 family house. Anyhow, just seeing if there is any feasability to somehow utilizing this space….