The difference between Ohio's crystal cave and other more standard caves may not be, at first, apparent.
The key difference is that you are not in fact inside cave, so much as wandering within a single rock. Crystal Cave is the world's largest geode.
Discovered in 1887 by workers digging a well for winery operator Gustav Heineman, Heineman found that the cave was in actuality a "vug" or large cavity within a single rock. Three foot long Celestine crystals emerge from the walls. The cave is actually much larger, and likely less beautiful, today then it once was as many of the celestine crystals were mined for use in fireworks.
The cave is best toured drunkenly as part of the overall Heineman winery tour.