This is a picture of an exhaust port on the first Death Star.
Shafts for venting heat from reactor cores were known as thermal exhaust ports. Located within a mountain, the secret Imperial training facility on Daro possessed a thermal exhaust port that served as one of only two possible ways to exit the base. However, due to the extreme drop outside the port, exiting this way without flying transportation was not recommended. Notably, the Death Star space station contained two such ports: a primary port and a smaller port that led directly to its reactor. Galen Erso intentionally designed this vulnerability as an act of sabotage, making the station critically weak. During the Battle of Yavin, Luke Skywalker, with the assistance of the Force, launched two proton torpedoes into the exhaust port, resulting in the battle station's destruction.