Seventh Door
The Seventh Door was the seventh entrance to the Matrix, a gateway that allowed living beings physical access to it. The Door could only be opened by the Key of Rassilon and was located outside the courtroom on Space Station Zenobia. (TV: The Ultimate Foe)
Narvin heard stories of people who had passed through the Seventh Door into the Matrix and reported visiting impossible environments. (AUDIO: Damned If You Do [+]Loading...["Damned If You Do (audio story)"])
During his trial on, the Keeper allowed the Sixth Doctor through the Seventh Door to acquire evidence for his defence and meet with Anosia inside a closed sector of the Matrix. (PROSE: Interstitial Insecurity)
Towards the end of the trial, the Valeyard fled into the Matrix through the Seventh Door using a copy of the Key of Rassilon once his identity was revealed by the Tremas Master. He was followed by the Sixth Doctor, Sabalom Glitz, and Melanie Bush, the Doctor and Mel later exiting through the Seventh Door after the Valeyard's plans were thrawted. (TV: The Ultimate Foe)