From the Middle Ages until the 1800s this area was excavated for ‘mill stones’ for the numerous mills in the region. The activity left strange patterns on the rock and led to the creation of this man-made cave known as Hohllay. [source]

Hohllay (“hollow rock”) is located in Berdorf, a commune and small town in eastern Luxembourg. The area is a popular destination for hikers and the cave measures about 360 square meters (3,875 sq. ft).