Stretching over four sandy kilometres Almanarre beach in southern France is a mecca for sun lovers and kite surfers. But its greatest treasure -- a 2 000-year-old underwater archaeological site -- lies just a few feet offshore.

The ruins of the city of Olbia are visible above the ground too, but it's the underwater ruins that are unique and intriguing. The city was first Greek, the invaded by Rome, and was inhabited for about 1 000 years.