It looks like the rampart of a dropoff in The Bells near Dahab in the Red Sea.
http://www.sinainet.com.eg/Diving/Da...tes/The_Bells/
Just got a monofin myself, looking forward to learning about the performance in the open ocean. It sure is fast in a pool.
Palancar in Cozumel has cave features like this along the wall as I recall. Interesting stuff!