There are two locks on my apartment door. The key to the bottom lock was lost long ago - before I moved in - and we now just use the top lock.
The bottom lock is probably 50-60 years old and doesn't have any identifying information on its exterior. It works fine. We just don't use it because we don't have a key.
Once, when a locksmith was here working on the other lock, I asked him about it, but he just tried to sell me a replacement, which was going to be very expensive.
Is it possible to have a new key made for an old lock? What would be the challenge in a case like this - is there any reason it would be easier to just replace the whole thing?