This is a Marble Cave in Cuevas de Marmol, Chile. The Marble Caves is geological formation of unusual beauty. These caves have formed in a pure marble and are bathed in the deep blue water of General Carrera Lake. The enormous General Carrera Lake is fed by rivers coming from several glaciers of Patagonian Andes. The ice of glaciers contains small particles and, when the ice melts, many particles remain suspended in the water. This gives an unusual effect - the glacial meltwater is slightly turbid and it refracts the blue part of sunlight. Due to this the water of General Carrera Lake has a distinct blue color. It has been calculated that the whole block of marble weighs 5 billion tons. The stone is in light grey color, with frequent darker striation. In some places boats go under the ground, through marble tunnels. Naturally, in bad weather boats can not drive near the caves. http://www.wondermondo.com/Countries/SA/Chile/Aisen/CapillaDelMarmol.htm