TARDIS

Short for Time and Relative Dimension(s) in Space. An ingenious cross between a time machine and a spaceship, whose chief characteristics apart from their travelling abilities aforementioned are that they (usually) have the ability to change form to blend in with their surroundings (the Doctor's doesn't, but that's another story), and that their interiors are perceptually usually bigger than their exteriors, because the interiors are on a subtly different dimensional plane to the 'real' world around them.

At least, I think that's the case. TL

Doctor Who