Diamond Caverns. On July 14, 1859, a slave was lowered into a pit discovered on the farm of Jesse Coats. He saw glistening calcite crystals that he thought were diamonds. The first public tour was made by a wedding party on August 19,1859. Guidebooks were written about the cave and its beautiful limestone formations. Over (Reverse) The cave is famed for its pristine cave formations, and was shown with Mammoth Cave in the late 1800s. Mammoth Cave Railroad ran nearby. Passages found in 1936 doubled the length of the cave. It is the second-oldest show cave in Kentucky and the fourth-oldest continuously visited commercial cave in the United States. Over