Celestial Omnibus

Iris Wildthyme's TARDIS, known as the Celestial Omnibus, resembled a red London double-decker bus, specifically the Number 22 to Putney Common.

Appearance
The Celestial Omnibus took the form of a red double decker bus - The 1963 AEG Routemaster RML with non-standard concertinaing doors - to be precise. (PROSE: Iris Wildthyme and the Unholy Ghost)

Unlike other TARDISes, it was slightly smaller on the inside than on the outside. (PROSE: The Scarlet Empress)

According to one source, the bus was not actually smaller than other TARDISes, but instead most of its interior dimensions were used to store water. (PROSE: Verdigris) However, by some accounts, the bus actually got its water from a space-time link to a Canadian lake in 1924. (PROSE: Enter Wildthyme, The Scarlet Empress)

The inside looked like a modified double-decker bus, though with a few hints of its true nature. (PROSE: Old Flames) The TARDIS had a small kitchenette in the back, a shower and a wardrobe upstairs. The controls were on the dashboard. The controls resembled those of the Doctor's TARDIS during his eighth incarnation. (PROSE: The Scarlet Empress, Enter Wildthyme)

The lower floor of the bus contained a record player and a rack of records, including some by Tammy Wynette. (PROSE: Future Legend) Iris also had a collection of tapes, including a Geoff Love rendition of the Doctor Who theme, various songs by Shirley Bassey (PROSE: Bafflement and Devotion, Enter Wildthyme), Vince Cosmos, and Lady Marmalade (PROSE: Enter Wildthyme) There was also a drinks cabinet. (PROSE: Old Flames)

History
Iris found the bus during her youth in the Obverse, where it had crashed, and breathed new life into it. She then left the Obverse in the bus into the universe beyond. (PROSE: Wildthyme Beyond!)

Iris once had Christmas dinner with Fifth Doctor, Tegan Jovanka, and Vislor Turlough in the bus. (PROSE: The Scarlet Empress)

When the Obverse was altered to be a bit more steampunk, the omnibus was transformed into an airship. (PROSE: Flasket Brinner and the Clockwork Heart et al) On one occasion, a member of Faction Paradox fused Panda with the airship. (PROSE: Panda and the Airship)

Fate of the Omnibus
In a possible future, Iris had changed into Bianca — Iris' own version of the Valeyard. Bianca converted her breaking-down TARDIS into a nightclub, planning to snare Iris and take her remaining regenerations. The Sixth Doctor used his own TARDIS as a time ram to destroy the club. (AUDIO: The Wormery)

Iris once rammed the bus into the City of the Saved's sealed Uptime Gate to save her companions from the Civil War. The fate of Iris and the bus was uncertain, (PROSE: A Hundred Words from a Civil War) but Cortalian once auctioned off a piece of timeship in the shape of a passenger bus gear shift which had been blasted down into history after colliding with the City. (PROSE: Going Once, Going Twice)

Near the end of the universe, PussyWorlders discovered the omnibus abandoned in the ruins of a Hyspero car park. They were unable to use it, as it seemed dead, but managed to snap off a loose piece of the drive system. (PROSE: Future Legend)

Undated events
Jack told Ace that hippies helped put Panda on "the bus to space". (PROSE: Teenage Kicks)1

Behind the scenes
Perhaps coincidentally, the number 22 to Putney Common appeared briefly in the opening scenes of Rose, the only time an allusion to the Celestial Omnibus or Iris Wildthyme has been made on television to date. On the cover of Iris Wildthyme and the Polythene Terror published in 2019, the design of the Celestial Omnibus matched that featured in Rose with two identical adverts for The Lion King.