we were walking deep in the woods in my hometown at the time MD. came upon a cave covered by a large boulder, came back later in the evening around dusk and the boulder had moved to allow whatever passage in or out,this boulder was huge with no possible road or passage to get any heavy machinery to the area to lift the 10' oval boulder that weighed several tonnes...wtf? my friend and I jogged the next couple miles to our car taking turns looking behind us...