This is a natural limestone cave. One of my favorite places to visit. The easiest way to get there is by canoe. One "floats" down the Meramec River and the cave is located in a huge bluff by the river's edge. There is a small stream that flows out of the cave into the river. This time I didn't canoe in but walked in. There is no clear trail to this cave which generally discourages people from walking there.