Ganh Da Dia, which means Sea Cliff of Stone Plates, is a seashore area of uniformly interlocking basalt rock columns located along the coast in An Ninh Dong Commune, Tuy An District, Phu Yen Province in central Vietnam.
The area is about 100 meters wide and 250 meters long, composed of an estimated 35,000 columns of basalt rocks. The rocks are dark lava columns with roughly flat surfaces of different shapes - round, pentagon, hexagon, polygon...
Ganh Da Dia looks like a gigantic beehive or pile of dinner plates, hence the name.
The rock columns were created from volcanic eruptions millions of years ago; when the molten basalt flows met cold water, they solidified and created polygonal formations due to thermal contraction.
Ganh Da Dia was listed as a National Heritage site in January 1998 by the Ministry of Culture, Sports and Tourism.