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)

During his trial on, the Keeper allowed the Sixth Doctor through the Seventh Door to acquire evidence for his defense 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 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)