Well, Daniel found a few dozen keys but none of them fit the banjo case, so we finally just unscrewed the one catch that was locked. There's a pretty nice banjo in there. I tried playing it for a bit but the whole 5-string thing was confusing me, so I think I'll just stick with the accordion for now. Of course, that's somewhat confusing as well, but I'm having more fun with it.
Among the other interesting things that can be found in this house: a set of bagpipes, a dark lamp, and a real-time pitch-adjusting telephone.