Detroit is a truly incredible city, and a place I highly recommend everyone visit. You'll find great food, beautiful architecture, wonderful people and vibrant art scene that can surprise you in unlikely places. We stumbled across this inverted marble mound while exploring the the train station that was abandoned in the 80's. the structure itself is pretty astounding, but the artist had gone as far as to add welded steel beams on the floor beneath the mound to make sure the floor could support it's weight.