Just about every worthwhile destination has a claim to fame. For one Missouri cave, it has several. One includes a rubber duck that has called it home for over 75 years. Oh, and it (the cave) serves burgers, too.
Having lived in or near to Missouri a majority of my life, I've been in just about every cave in the state. However, even with my spelunking past, there's one that's just hit my radar that I had never heard of and I'm thinking it's possible you might not have heard of it either.