Jefferires tubes:
On Starfleet vessels, Jefferies tubes are internal maintenance conduits that are used to provide crew access to various ship's systems. In emergencies they're also used for moving around the ship if turbolifts are not functional. Doors within the Jefferies tubes can be sealed for safety or security reasons. It should be noted that on all ship displays of internal structure Jefferies tubes are not displayed, and in some cases show no sign where they could actually fit within the ship.