Shada

Shada was the "prison planet" of the Time Lords, locked in a bubble outside the universe, (PROSE: Shada) for would-be conquerors of the universe. (WC: Shada) According to some accounts, it was an literal prison planet; (COMIC: The One) according to other accounts, it was just a planetoid or asteroid, although even then it was sometimes referred to as a planet. (PROSE: Shada, Doctor Who and the Krikkitmen, AUDIO: Shada)

Features
The prison was both locked in a bubble outside the universe and time-locked. (PROSE: Shada) It was contained by a quantum wall and its surface was patrolled by robot guardians. (COMIC: The One) All of the Spiral Politic could be seen moving through its history from a viewing area in the prison. (AUDIO: A Labyrinth of Histories)

The prisoners of Shada were stored each in their own separate cryogenic cell, alive, but frozen in time, in perpetual imprisonment. (PROSE: Shada) Prisoners had dragon tattoos which snapped upon their release. (PROSE: Christmas on a Rational Planet) The Thirteenth Doctor noted that Shada was "esigned so that once you're in you can never find your way out". (PROSE: The Secret in Vault 13)

During the War in Heaven, when the Great Houses began using their prison planet more often, War criminals began to fit themselves with ice-proof secondary nervous systems to help them in case they were sent there. Realising that this made it too easy to break out of cryogenics, the Great Houses started directly linking prisoners' nervous systems into self-repeating time-frames through the convict tattoos on their upper right arms. (AUDIO: Movers)

The prison stored a "backup" history of the Homeworld as a safety feature should the Great Houses be destroyed or erased from time. The prison also had a access to the Great Houses' records library. (AUDIO: A Labyrinth of Histories)

Despite its foreboding nature, Shada also contained a gift shop where commemorative T-shirts could be purchased by anyone who, against all odds, managed to leave. The Doctor owned one such T-shirt. (PROSE: The Secret in Vault 13)

Early history
Shada was created in the days of Rassilon; the key to Shada, a decoy book known as The Worshipful and Ancient Law of Gallifrey, was considered one of the Artefacts of Rassilon. (TV: Shada)

Shada was used the early Time Lords to imprison dangerous members of other species. (PROSE: Doctor Who and the Krikkitmen, etc.) For example, five million Krikkitmen were stored in their own dimension on Shada after the Krikkit War. In a later era, while visiting Shada, the Doctor also saw Sontarans, an Ice Lord and a Krarg among the inmates, (PROSE: Doctor Who and the Krikkitmen) as well as numerous Daleks. (WC: Shada)

The Time Lords also imprisoned many of their own number who devolved into dangerous megalomaniacs in Shada. (COMIC: The One) The Heretic was either killed by the Time Lords or imprisoned on Shada after plotting to regenerate the universe. (AUDIO: The Two Masters) While searching for Salyavin, Skagra accessed the records of war criminal Rungar and mass-murderer Sabjatrik who were also prisoners in perpetuity. (WC: Shada, AUDIO: Shada) According to one account, Lady Scintilla was imprisoned in Shada for "conspiring with Carrionites". (PROSE: Shada) Among the last of this category during the prison planet original span of use was Grandfather Paradox, who was sent to the prison planet shortly after the Renegade Presidency affair, as part of a generalised crackdown on "interventionists" and other "subversive elements". (PROSE: Crimes Against History)

was also imprisoned there until the wardens intentionally allowed him to escape so that he could keep the Third Doctor busy during his exile on Earth — as per the Celestial Intervention Agency's plans. (PROSE: Prisoners of the Sun) The Doctor was instead told that the Time Lords hadn't managed to capture the Master following the War Games affair, only barely being able to track him to Earth. (PROSE: Doctor Who and the Terror of the Autons)

Forgotten
At some point, Salyavin, a Time Lord with unusually powerful abilities of telepathic control, was condemned to be imprisoned on Shada. Although he was remembered by the likes of the Fourth Doctor as having been a genuine Renegade in his day, with the nom de guerre of "the Great Mind Outlaw", (TV: Shada) some accounts suggested he was innocent, having only used his powers for a few harmless pranks, (PROSE: Shada) and was sentenced to imprisonment in Shada either because he had been framed by his own student the Master for an attempted breach of the Panopticon Archive, (PROSE: The Legacy of Gallifrey) or simply because some high-ranking Time Lords we afraid of what he might imaginably do with his abilities, despite his obvious disinterest in pursuing political power. (PROSE: Shada) At any rate, Salyavin would prove to be the last new inmate at Shada for a long time. Escaping his captors as he was being transferred to the prison, he used his powers to craft a new identity (the innocuous Professor Chronotis) for himself and erase all memory of Shada's existence from Gallifrey, so that his absence from his cell could never be noticed. (TV: Shada, PROSE: Shada)

Rediscovery
After discovering Gallifreyan records on his home planet of Drornid, which had once been under the control of a renegade Time Lord Presidency, the Drornidian scientist Skagra sought Shada out with the intention of freeing Salyavin and using his sphere to extract Salyavin's mental powers for his own use. Stealing The Worshipful and Ancient Law of Gallifrey from Professor Chronotis without realising he and Salyavin were one and the same, Skagra forced the Fourth Doctor and Romana II to use the Doctor's TARDIS and the book to take him to Shada. There, he broke out a number of prisoners, using his spheres to control their minds, but he was ultimately defeated. (PROSE: Shada)

The Fourth Doctor later borrowed The Worshipful and Ancient Law of Gallifrey' from Chronotis again and returned to destroy the Krikkitmen imprisoned there, but a few other, already-escaped Krikkitmen let them out instead. (PROSE: Doctor Who and the Krikkitmen)

During Romana's Presidency
With Romana II ultimately becoming President of the High Council herself, the Time Lord leadership once more knew about Shada. (PROSE: The Book of the War) For example, at a point prior to W-Time, they sent the Gentleman to "their prison" after he proved too hard to control. (PROSE: Ring Theory)

However, Romana's knowledge of Shada also had unexpected results when, due to an epileptic fit brought on by the coming of the Carnival Queen, President Romana ordered three hundred of Shada's most dangerous prisoners, including Grandfather Paradox, set free. (PROSE: Christmas on a Rational Planet) He promptly cut his arm off, thus freeing himself of the prison tattoo by which he might have been tracked down again, and announced the transition of House Paradox into the more recognisable modern form of Faction Paradox. (PROSE: The Book of the War)

At some point, as a knock-on effect of Borusa's interference with the Fourth Doctor and Romana II's holiday in Cambridge using the Time Scoop, (TV: The Five Doctors, WC: Shada) time was altered so that the Doctor and Romana's original adventure rediscovering Shada had not occurred. Sensing that something was amiss with time, the Eighth Doctor met up with the older, now-President Romana and convinced her to pick up where they left off all those years ago. In this new version of events, it was only at that point in their respective lives that the Doctor and Romana rediscovered Shada and the truth about Salyavin. Zaphod Beeblebrox and at least two versions of Arthur Dent were also imprisoned in Shada by this point. (WC: Shada)

During the War
Although Grandfather Paradox erased himself from history shortly after his escape, with the Faction Paradox acting in the War without his direct leadership, (PROSE: The Book of the War) attempts were made to force "the Grandfather" to finish his sentence all the same. After the Grandfather's shadow was bonded to Cousin Justine, she was tried by the ruling Houses in place of the Grandfather and sent to the Prison Planet. (AUDIO: In the Year of the Cat) However, she was ultimately rescued. (AUDIO: A Labyrinth of Histories) Devonire began his search for Grandfather Paradox's arm in the prison. After this quest sent him mad, until he started to believe that he was himself the Grandfather, the Houses decided to imprison him in the prison planet in perpetuity, on the off-chance that he was correct. (PROSE: The Book of the War)

Post-Time War incursions
The Eleventh Doctor visited Shada in search of the Master's first TARDIS (imprisoned there after the Last Great Time War), thinking had framed him for the downfall of the Overcaste. The Doctor, alongside Alice Obiefune, Abslom Daak, and the Squire visited Stormcage Containment Facility to retrieve River Song, whom the Doctor believed could help enter Shada and find the TARDIS. After obtaining a stargate he left for himself which led the path to Shada, the Doctor and the others entered by crashing the Then and the Now onto the quantum wall containing the prison. Although the Doctor forced himself to forget the planet's name so he would not be tempted to return, upon arriving there, he remembered it. (COMIC: The One)

Behind the scenes

 * Douglas Adams originally came up with the idea of a Time Lord prison as a location to store the Krikkitmen in his draft for the story The Krikkitmen. When that script was rejected he reused the idea for Shada. James Goss noted this in the appendix to the novelisation, where he used Shada for the same purpose in the story.
 * Shada title.jpg the unaired serial, Shada was originally going to hold a Dalek, a Cyberman and a Zygon, but the scenes set in Shada's interior were never recorded.
 * The completed TV serial had the recognisable shadows of some aliens in its cells including an Ice Warrior and a Zygon.
 * The webcast illustration of Shada's interior contains several Daleks, as well as Arthur Dent and Zaphod Beeblebrox from The Hitchhiker's Guide to the Galaxy as a nod to Douglas Adams.