This is a picture of a pond I first encountered on google maps. It was next to an exit off 394 that I take all the time. But I had never seen a pond there! I later found it when I was riding my bike. This little pond can't be seen from the road because its so close to the (walled) exit, it's almost under the pavement. I inverted the image to work with the title, and to give it that underworld/otherworld feeling it gave me when I first found it.
Under the Concrete is also a reference to the non-visible world...everything beyond what we percieve to be "real" or "concrete"