The Capitol, since there are other capitols in the DWU.
Talk about it here.
The Capital was the home of the Time Lords on Gallifrey. (TV: The Deadly Assassin) It was also known as the Citadel. (TV: The Invasion of Time, The Sound of Drums) The Capital was built on the remains of the original Capital which was destroyed in the Gallifreyan Civil War. (AUDIO: Lies)
The Capital stood in the mountains of Solace and Solitude on the continent of Wild Endeavour. (TV: The Sound of Drums) It was enclosed in a "mighty glass dome". (TV: Gridlock) It rested on a large, vertical beam, with a wheel-like structure securing it while it overlooked other complexes on a lower level. (TV: The Name of the Doctor, The Day of the Doctor)
At least two shanty towns existed just outside the Capital's dome, named Low Town (PROSE: The Eight Doctors, The Infinity Doctors) and MidTown (PROSE: The Ancestor Cell), and inhabited by Gallifrey's poor and the Outsiders. (PROSE: The Eight Doctors, The Infinity Doctors) Low Town led directly into the "Outlands" (PROSE: The Eight Doctors) or drylands, (TV: Hell Bent) while MidTown was on a mountainside overlooking the Capital. (PROSE: The Ancestor Cell)
Under the Capital, according to the Third Doctor, there were structures or settlements called New Towns, inhabited by Gallifreyan "commoners." (PROSE: Verdigris)
The Panopticon was the main room of the Capital, where the Eye of Harmony was secretly kept far below. (TV: The Deadly Assassin)
The High Council met in the Capital. There was a transmat system that linked the Council's room to the Death Zone. (TV: The Five Doctors) Also on Gallifrey was the Time Lord Academy. (TV: The Sound of Drums)
The Towers of Canonicity and Likelihood lorded over the northern part of the Capital. (PROSE: The Blue Angel)
The Vaults were located underneath the Capital. (AUDIO: Lies) The Vaults contained the ruins of the original Capital, a graveyard for TARDISes (PROSE: Engines of War) and the Cloisters, which housed the Matrix and Cloister Bells. (TV: Hell Bent) Surrounding the Vaults were ducts and serviceways dating from the Old Time. (TV: The Deadly Assassin) By the time of the Doctor, they were used by those who worshipped shrines dedicated to the cult of "Rassilon the Vampire". (PROSE: Goth Opera)
There was a repair shop in the Capital; among the items there were TARDISes. Two technicians, Andro and Fabian, were working there when the First Doctor, with his granddaughter, stole a faulty Type 40 TARDIS. They observed the event. (TV: The Name of the Doctor)
The Imperator offered Thessalia the role of chatelaine of the citadel. (PROSE: The Return of the King)
The Capital was "flooded" by Quarks in an invasion attempt by the Dominators. The invaders were fought by Leela and K9 Mark I, who destroyed 39 between them. Though the invasion was thwarted, one of the Quarks was fitted with a bomb which damaged the Capital heavily, necessitating the construction of a replacement building. (AUDIO: Time in Office)
By the Last Great Time War, the Capital had expansive but minimalist spaces with metal walkways, a darkened conference room, and a huge council chamber with Time Lords standing on suspended platforms. By the final day of the War, the Citadel was severely damaged by Dalek Saucers. The crashed saucers remained on the surface next to the Citadel. (TV: The End of Time) Following the Fall of Arcadia, the Capital became at risk with Dalek forces converging towards it. This danger was detected in the War Room of the Capital, where the General drew up stratagems with his associates. The Time Vaults contained the Omega Arsenal, where, on the final day of the War, the Moment was stolen from by the War Doctor. (TV: The Day of the Doctor)
After the end of the war, the Capital was repaired with all signs and evidence of the Time War removed. (TV: Heaven Sent)
Layout
The Capital was divided in eight "sectors".
Sector 1's main tower housed the Panopticon, a vast hexagonal chamber in which great events of state were held. Elsewhere in the tower was the Capital Museum, where the symbols of presidential office were on display, along with examples of every kind of robe of state, from the President and the Gold Usher to the Chapter Cardinals.
Sector 2 was the political heart of the Capital, housing an enormous assembly room for meetings of the full High Council, a conference room for the Inner Council and other small gatherings, and the President's office.
Sector 3 was entirely dedicated to the Chancellor and the Chancellery Guard.
Sector 4 contained the Castellan's office, the courtrooms, and the Security Compound, which itself comprised detention rooms, interrogation cells, and several execution rooms, most of which were officially disused.
Sector 5 comprised hundreds of libraries, records rooms and archive stores.
Sector 6, which housed the various Chapters of the Time Lord Academy and the main force-field control area for the transduction barrier that shielded Gallifrey, was the largest structure in the Capital after the Panopticon.
Sector 7 was dominated by the Communications Tower, from which Space Traffic Control and Temporal Control monitored and logged every passing vessel in Gallifrey's vicinity. It was also rumoured to be the site of Gallifrey High Command's War Room, together with an extraction chamber — although the existence of such chambers was officially denied.
Finally, Sector 8 was home to the Time Travel Capsule landing bays and an array of repair shops. Below the repair shops was an area known as the TARDIS Graveyards, where TARDISes that reached the end of their lifespans were despatched. Somewhere in the citadel, a set of chambers were allocated to the Celestial Intervention Agency, but no one outside the Agency knew exactly where those chambers were. Deep beneath the Panopticon were the Panopticon Vaults, where the Eye of Harmony was kept.
Deeper still were the Cloisters, the physical location of the Matrix, guarded by the Cloister Wraiths. Finally, buried near the very core of Gallifrey were the Time Vaults, where all the forbidden weapons of the Omega Arsenal were locked away. (PROSE: A Brief History of Time Lords)
Behind the scenes
Though this was not directly contradicted or affirmed by the Graham Williams-produced TV story, the novelisation of The Invasion of Time describes the Capital as covering "most of Gallifrey" and being surrounded by a sheer white wall.
A dome was first associated with Gallifrey in the header art for Doctor Who Magazine's "Gallifrey Guardian" section; this was later shown to be covering the Capital in DWM comics like The Tides of Time, and Peter McKinstry used it when designing the Capital for The Sound of Drums. "With the citadel it was an opportunity to take elements of the very organic TARDIS interior and apply them on a much grander scale," he recalled. (ImageFX magazine, October 2008, p. 62) This image of the Capital as a regular-sized city surrounded by a transparent dome was used in various episodes under showrunners Russell T Davies and Steven Moffat, including a scene in The Name of the Doctor set before the First Doctor left Gallifrey.
No buildings or settlements were seen immediately outside the dome in pre-Time War flashbacks from the Davies-era story The Sound of Drums or the Moffat-era story The Name of the Doctor; nor were they seen in the Davies-era story The End of Time, which was set during the Time War. Several tall constructions appeared beyond the dome and the wheel-shaped structure it sits on during and after the Time War in the Moffat-era stories The Day of the Doctor, Heaven Sent, and Hell Bent.