The six great north faces of the Alps are a group of vertical faces in the Swiss, French, and Italian Alps known in mountaineering for their difficulty, danger, and great height. The "Trilogy" is the three hardest of these north faces, being the Eiger, the Grandes Jorasses, and the Matterhorn.

In geography and geology, a cliff is an area of rock which has a general angle defined by the vertical, or nearly vertical. Cliffs are formed by the processes of weathering and erosion, with the effect of gravity. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually composed of rock that is resistant to weathering and erosion. The sedimentary rocks that are most likely to form cliffs include sandstone, limestone, chalk, and dolomite. Igneous rocks such as granite and basalt also often form cliffs.