Iris Wildthyme's TARDIS, known as the Celestial Omnibus, resembled a red London double-decker bus, specifically the Number 22 to Putney Common. 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!) Unlike other TARDISes, it was slightly smaller on the inside than on the outside. (PROSE: 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)

The lower floor of the bus contained a record player and a rack of records, including some by Tammy Wynette. (PROSE: Iris Wildthyme and the Celestial Omnibus ^{[additional sources needed]}) There was also a drinks cabinet. (PROSE: Old Flames)

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)