Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A half-pipe is a structure used in gravity extreme sports such as snowboarding, skateboarding, skiing, freestyle BMX and inline skating. The structure is usually wood, although sometimes the surface is made of another material such as concrete, metal, dirt or snow. In appearance, it resembles a cross section of a swimming-pool, and in its most basic form, it consists of two concave ramps (or quarterpipes), topped by copings and decks, facing each other across a transition.