Nea Kameni

Dive on a very new volcanic island (it last erupted in 1956) in the center of an old exploded volcano, who's caldera is open the sea. There isn't a lot of life, but the water is clear, and there are some quite interesting lava formations here. The bottom in the crater drops away to hundreds of meters... The 34 m long steel wreck lies at 13 m in the harbor, and is actually visible below the surface in the Google Maps photo, so it isn't hard to find.