Arch in the Sky is a spectacular natural arch located on In-Ahtim site to the west of the Idou Sites on the vast Tassili National Park in Algeria. This well-hidden double arch has a measured span of 12 meters and the second opening below has a span about 4.2 meters. The thickness of the thiny lintel has 20 centimeters (8 inches) and the wide is about 60 centimeters  (24 inches) where stands the author. GPS coordinates 24°50.526' 9°29.381'