The Matrix Chamber, (AUDIO: Neverland, TV: The Timeless Children) or Great Matrix Chamber, (PROSE: Doctor Who and the Krikkitmen) was a room in the Citadel used to access the Matrix. (TV: The Timeless Children)
The Fourth Doctor and Romana II once visited the Great Matrix Chamber. (PROSE: Doctor Who and the Krikkitmen)
During the anti-time crisis of Romana's presidency, the Matrix Chamber was connected to the Time Station. (AUDIO: Neverland)
The Spy Master took the Thirteenth Doctor to the Matrix Chamber. (TV: The Timeless Children)