Catwalk
The catwalk was the unofficial designation for the lateral access conduit running the entire length of the warp nacelles of an  starship. Located at the center of the nacelle, just below the ship's warp coils, the catwalk was accessible through a single vertical Jefferies tube.

Protected by an outer shell composed of an osmium alloy, the catwalk was used as a maintenance shaft, though it was only operative if the ship's warp drive was shut down. With warp systems online, the catwalk was subject to extreme high temperatures and was not suitable for habitation. The catwalk was divided into several compartments. ()

In 2152, the crew of the starship  took refuge from a deadly neutronic storm within the catwalk. Utilizing a makeshift command area which the ship's Chief Engineer Commander Charles Tucker III prepared, Captain Jonathan Archer, First Officer T'Pol and Helmsman Travis Mayweather were able to control Enterprises navigation through the storm. ()

Later in 2152, Archer once again led his crew into the catwalk when Enterprise was invaded by non-corporeal beings. Unable to penetrate the catwalk's protective deflector shielding, the beings were kept at bay long enough for Archer and his crew to repel their attack. ()

In January 2153, Mayweather told his mother, Rianna, about how the crew had, a few months beforehand, needed to "squeeze into one of the nacelles for a couple days" due to a storm. ()

The  also possessed a catwalk. In 2368, when Lieutenant Commander Geordi La Forge experienced dizziness due to a phase shift in his visual receptors caused by the ship being in a temporal causality loop, he stated that at first he thought the catwalk was spinning. ()

See also 
 Jefferies tube
 Emergency access conduit
 Maintenance shaft
Spacecraft sections