The Cardassians called it Terok Nor, but we know it as starbase Deep Space 9, Star Trek: Deep Space Nine's titular 45,000,000 metric ton, 1,452 meter-wide bicycle wheel in space.
For seven seasons, Captain Benjamin Sisko and his combined Starfleet, Bajoran, and civilian cohorts inhabited DS9, situated perilously close to the Bajoran Wormhole and the gateway to the Gamma Quadrant. Over those seven years, much of the station was explored, but most of the action was relegated to the familiar locations of Ops, the Promenade, Quark's bar, crew quarters, and docking ring.
The series gave us tantalizing glimpses of the station's larger infrastructure and inner core, but many of the former Cardassian ore processing facility's secrets still remained within her duranium composite walls by the end of show's run.
With Rick Sternbach and Doug Drexler's Star Trek: Deep Space Nine Technical Manual thoroughly dog-eared (vole-eared?), here are all the secrets and quirks of starbase Deep Space 9 the Cardassians have been hiding from us.
10. DS9's First Appearance
Star Trek: The Next Generation's season six two-parter "Chain of Command" was initially intended to crossover with Star Trek: Deep Space Nine's first year, featuring a visit to the station and a guest appearance by Quark. However, release schedules changed, placing "Chain of Command, Part I" well before DS9's premiere, requiring the removal of Quark and any explicit references to the new show.
However, while the scenes that were intended to take place aboard the station were shifted to the planet Torman V, Star Trek: Deep Space Nine's sets were nevertheless used to film the episode. In the episode, undercover Picard, Worf, and Crusher go to a seedy bar on Torman V to meet with Daimon Solok (Quark's replacement in the script), with the production utilizing a redressed version of DS9's replimat set.
As "Chain of Command, Part I" aired nearly a month before DS9's "Emissary", this is the first on screen appearance of space station Deep Space 9, despite its use as another locale in the Star Trek Universe.