Jefferies tube

On Starfleet starships, Jefferies tubes are internal maintenance conduits that are used to provide crew access to various ship's systems. They also carry the bulk of the utilities trunks and circuitry through every corner of a ship. In emergencies they can be used for moving around the ship if turbolifts are not functional. Doors within the Jefferies tubes can be sealed for safety or security reasons. Normally, the tubes only allow room for an average humanoid to crawl around in, although maintenance/diagnostic junctions are big enough for personnel to stand in. They can run both vertical (with built-in ladder rungs) and horizontal.

Jefferies tubes can also be used for fitness training exercises.