Iris Wildthyme's TARDIS resembled a red London double decker bus, specifically the Number 22 to Putney Common. Iris claimed that she rescued her TARDIS from scrap and nursed it back to health.
Unusually, it was slightly smaller on the inside, than on the outside. (Other TARDISes were commonly bigger on the inside than on the outside.) It shares this quality with the Machine.
The TARDIS had a small kitchenette in the back, a shower and a wardrobe upstairs. The controls were on the dashboard. The controls had a resemblance to that of the Doctor's TARDIS during his eighth incarnation. (EDA: The Scarlet Empress)
The lower floor of the Bus contains a record player and a rack of records, including some by Tammy Wynette. (BFA: Iris Wildthyme and the Celestial Omnibus)