
Rigel VII fortress

Fortress of Doom
A fortress was a military fortification.
On the Torothan homeworld in February 2152, Captain Jonathan Archer and Commander Charles "Trip" Tucker sought refuge in an abandoned fortress. It was eventually destroyed by a Torothan mortar, though Archer and Tucker had fortunately left by then. (ENT: "Desert Crossing")
Captain Christopher Pike felt guilty for becoming trapped in a deserted fortress on Rigel VII due to his error in judgement, a mistake which lead to the death of three people including his yeoman and the wounding of seven more. (TOS: "The Cage", "The Menagerie, Part I") The same fortress later appeared in a simulation he and Vina were subjected to by the Talosians. (TOS: "The Cage", "The Menagerie, Part II")
When Spock's tricorder readings found the Shore Leave Planet to be composed of granite and metal alloy, James T. Kirk said the planet was built like a fortress. (TAS: "Once Upon a Planet")
Kirk declined Em/3/Green's suggestion that he use his phaser to fight Tchar, saying that the Skorr controlled the fortress phaser bank. (TAS: "The Jihad")
When Ensign Ro Laren told Kalita her plans to steal medkits from the USS Enterprise-D, Kalita wondered how she could do it, describing the Enterprise-D as a fortress. (TNG: "Preemptive Strike")
A fortress was part of the late 20th century computer game Matrix of Doom. (VOY: "11:59")