Formed during the Würm glaciation (around 80,000 to 10,000 BC), Lake Longemer is one of the largest in the Vosges mountains. It was born from the Vologne glacier, which stretched over nearly 25 miles (40 km) in length. The lake is about 1,2 miles (2 km) long and extends between two wooded slopes of tall firs. A small chapel dating from the mid-15th century and dedicated to Saint Florent stands on the west bank. The area is classified as a natural site of the Vosges.