**Update: It is a more likely theory that these caves are a part of Joseph Bonaparte's escape tunnels from his mansion. He had built several tunnels from his home to the lake, these may have been additional routes as you can see in the video there are filled in tunnels inside the structures.
But other sources will have you believe very little is certain about the age and origin of these stone man-made caves. There are supposedly twelve of these in New Jersey, and some four hundred in all of New England.
