Buildering is basically bouldering on buildings instead of rock. Many buildings have interesting and very climbable features, however it’s worth pointing out that buildering is illegal in most countries. There is also a very obvious danger factor with buildering as the ascents are made without any ropes or protection.

Alain Robert on one of his famous “rope free” ascents.

Certain climbers have become famous for climbing some of the most famous skyscrapers in the world, using the features in the structure, or in some cases the window frames as climbing holds.