Lost city of Atlantis

Actually it's Akrotiri, a 3500 year old city on Santorini that was destroyed and buried when the island erupted. Excavations have been going on here since the 60s, but only a small tip of the city has been uncovered.

Some have hypothesised that Santorini may in fact be the location of the lost civilisation of Atlantis, destroyed by volcano. Others just think that Plato made the whole thing up.