Paula at Lost in Translation presented us a challenge for this month: traces of the past (Nature).
This photo was taken in Palma de Mallorca, in the Caves of the Drach (Cuevas del Drach)
The caves have formed by water being forced through the entrance from the Mediterranean Sea, and some researchers think the formation may date back to the Miocene Epoch. There is an underground lake situated in the caves called Martel Lake, which is about 115 m in length and 30 m in width, and its depth varies between four and twelve meters. It is named after the French explorer and scientist Édouard-Alfred Martel, who is considered the founding father of speleology (the study of caves). He was invited to explore the cave 1896. A German cave explorer, M.F. Will, had mapped the White and Black cave in 1880. Martel found two more caves, as well as the underground lake.(Wikipedia)