At an antique store, I bought a case to hold photo slides. For $15? I can't remember. Something low. But it already had some slides in it. The store owner offered to dump the slides into the trash for me. I said no, I'd keep them. Could be fun. Turned out they were taken by a solider stationed in Germany after WWII, circa 1952. They included pictures of Hitler's Eagle's Nest.
Those slides sold well on ebay. Paid for my little case many times over.
I think I've posted examples here before. Here's one -- at least I'm pretty sure that's what this picture is even though I don't see this view online.