Tunnel

A tunnel is a feature found on many roller coasters where a section of track is enclosed in a structure, or underground. Some tunnels have lighting effects, while others are kept in complete darkness.

Over-ground tunnels

Most tunnels are built above ground, mostly because they are cheaper to build and easier to maintain. Over-ground tunnels often have lighting effects.

Underground tunnels

As the name suggests, an underground tunnel is a segment of track built below the ground level of the roller coaster, and sometimes the park. These are often made out of concrete, and, depending on the intended atmosphere of the ride, may be lit or un-lit. Also, tunnels can go underwater, an example is Anaconda at Kings Dominion.

Oblivion at Alton Towers has one of, if not the deepest underground tunnel in a roller coaster.