My new old house has skeleton key locks throughout. The home was remodeled and had new locks added to the entry doors on the main floor to use, however the skeleton key setup is still there for looks.. Although it does work throughout the house and at every door still.
We have an unfinished basement with an exit door that has one of these old locks as well, but they didn't add anything new and so it honestly is the only way to open this door.
It was working last week when we were moving in and cleaning up, but now it's no longer working. The door is locked shut and whenever I put the key in, I can make it into the inner chamber and rotate the key somewhat both ways, but it comes to a stop and I can't get it to turn or anything. I could try forcing it, but I don't have anything, that I know of, that I could get in there that would be able to do the job. That and I don't know if the shape matters like modern keys.
I tried taking the cover off in hopes that this might give me some access to it, but it only removes the handle. I'll attach a picture below.