La Tour Percée (The pierced Tower) is a wonderful double natural arch located above Col de Marcieu (Marcieu Pass) on the cliff of Les Petites Roches near L'Aup du Seuil on Regional Natural Park of La Chartreuse in isère department of France. The largest opening has a measured span of 32 meters. The hiking and climbing route to the arch was pioneering by Pascal Sombardier (silhouetted on the opening) in may 2005. Can you image this arch totally unknow to the public until this time althrough the opening is situated only 25km distant from Grenoble center, a city about 400 000 peoples. It is amazing but it's true. IGN topographic map Top 25 number 3334 west La Chartreuse (pleat A9).