The Eighth Door was a matrix door that allowed one to physically enter the the Matrix. It was located onboard the Time Station and allowed Romana II to enter the Matrix and come in contact with Rassilon, (AUDIO: Neverland) before it was later moved beneath the control terminal for the Eye of Harmony in the Panopticon. (AUDIO: Renaissance)
In a version of the Doctor's TARDIS from an alternative universe, Ace found the Eight Door while wandering. Inside the dove-grey wall of roundels faded away into a rosy sunrise sky, the sun never seeming to set, while a wide expanse beach with calm, cold, white water lapping at its pebbled edge stretched into infinity. (PROSE: St Anthony's Fire)