A beach version of a butt groove. A dent, or groove, that has been hand (or ass) crafted, whilst one is relaxing or tanning at the beach, molded to fit the body.
You can make dents for your butt, Pillows for your head, ditches for breathing spaces when your lying on your tummy, the possibilites are endless!
One Dude *Laying on back wriggling bum into sand*
Another Dude: "Dude what are you doing?"
One Dude: "Im working on my sand groove!"