Strange Underwater Formations off the Zakynthos Coast

In 2013, snorkelers were exploring the waters off the coast of Zakynthos when they discovered what they first thought was an ancient Greek city. What they found were formations that lie between six to sixteen feet below the surface; they were assumed to be columns and the remnants of formerly paved roads.
Further investigations revealed that even though the formations and structures bear some similarities with ruins, what they really are is what’s left of a plumbing system located on the ocean floor; mineralization and hydrocarbon seeps have since occurred there.