When we think of the world's great museums, we tend to think of the Louvre, the Guggenheim or the Victoria and Albert. We do not immediately think of the Dog Collar Museum, the Kansas Barbed Wire Museum, the Museum of Broken Relationships or Barney Smith's Toilet Seat Art Museum. Yet scattered across the globe are museums dedicated to every conceivable subject, from bananas to Bigfoot, lawnmowers to leprechauns, teapots to tapeworms, mustard to moist...