Nea Kameni
The volcanic island of Santorini offers exciting scuba diving possibilities. One of the best spots is Nea Kameni, formed by an eruption, it last erupted in 1956. Dive on a very new volcanic island in the center of an old exploded volcano, whose caldera is open to the sea. There is not a lot of life, but the water is clear, and there are some quite interesting lava formations here. The bottom of the crater drops away to hundreds of meters.
Besides, the Santa Maria wreck is a 34m-long (112ft) steel passenger ship that sank in the Taxiarachis Bay in 1975. It is 18m (59ft) under the surface and is actually visible below the surface in the Google Maps photo, so it isn't hard to find. Therefore, it awaits all divers. The nearby waters also feature underwater lava formations and sea caves that are worth exploring.
Location: Santorini, Greece.