Off-road obstacle courses may be set up with a variety of different challenging situations. More common obstacles are hills, rockcrawling gates, log crawls, and mud pits. Some include underground tunnels, balance beams and water slides. Others are for the purposes of teaching high-speed driving on unimproved roads. Features include different kinds of turns, changes in elevation, navigating high speed straightaways and maneuvering vehicles through tight S-turns (so called because from above they resemble a letter "s").