Hang Sung Sot, or the "Cave of Surprises" in Ha Long Bay, Vietnam, was discovered in 1901 by the French. The cave is located on Bo Hon island.
One of the most popular in the bay with tourists, the cave requires a separate ticket to enter than the Thien Cung Cave ("Celestial Place") and Dau Go Cave ("Cave of the Wooden Stakes").
Hang Sung Sot is filled with unusual rock formations, which are highlighted by colored lights. These formations include a Buddha and a large tortoise, but the most well-known is a massive phallus in the cave's second chamber, which is lit by a pink spotlight.
The penis-shaped rock is known as a fertility symbol to locals.