Shada

Shada was the prison 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 a full 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 timelocked. (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)

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)

History
The villainous Skagra managed a successful jail break of the prisoners while in search of Salyavin, the notorious Time Lord criminal who had developed a means of projecting his own thoughts into anyone's mind. Skagra believed that with this power, he could impose his own thoughts and will on the universe. Salyavin, though, had already escaped and was living a peaceful life as Professor Chronotis of the University of Cambridge. (PROSE: Shada)

Five million Krikkitmen were stored in their own dimension on Shada after the Krikkit War. The Fourth Doctor eventually borrowed The Worshipful and Ancient Law of Gallifrey from Chronotis and returned to destroy them, but a few escaped Krikkitmen let them out. While on Shada, the Doctor also saw Sontarans, an Ice Lord, and a Krarg. (PROSE: Doctor Who and the Krikkitmen)

The Eleventh Doctor visited Shada in search of the Master's TARDIS (placed there after the Last Great Time War), thinking the Master 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)

Other notable prisoners
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) Arthur Dent and Zaphod Beeblebrox were also imprisoned. (WC: Shada)

Shada held other renegade Time Lords. The Master was 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)

Daniel Joyce had the tattoo of a prisoner of Shada. (PROSE: Unnatural History)

Grandfather Paradox was imprisoned on Shada. (Legend had it that he had been imprisoned rather than executed because "everyone was more afraid of him dead than alive".) Early during Romana's Presidency, she suffered an epileptic fit under the influence of the Carnival Queen and signed an executive order freeing three hundred prisoners from Shada, including the Grandfather, who led the freed prisoners. (PROSE: Christmas on a Rational Planet) When Cousin Justine was tried and convicted by the ruling Houses, since she held the Grandfather's shadow, she was sent to the prison-world to finish the Grandfather's sentence. (AUDIO: In the Year of the Cat) However, she was rescued. (AUDIO: A Labyrinth of Histories)

Devonire began his search for Grandfather Paradox's arm in the prison, and he was later imprisoned there in perpetuity. (PROSE: The Book of the War)

The Heretic was either killed by the Time Lords or imprisoned on Shada after plotting to regenerate the universe. (AUDIO: The Two Masters)

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.