A maintenance shaft was an area in a starship where access to the ship's internal systems and computer terminals was possible.
In 2153, two Tarkaleans assimilated by the Borg used a ladder from sickbay to gain access to maintenance shaft C, junction 12. There they removed several wall panels and accessed the avionics control system and the warp plasma regulators. A security team led by Lieutenant Malcolm Reed tried to stop the Tarkalean female but was attacked by the Tarkalean male. Captain Jonathan Archer chose to decompress the area and blew the drones through a hatch into space. (ENT: "Regeneration")