The pic below is of the Doctor's wonderful Time/Space vehicle, the Tardis. This section will give you info about the type 40 T.A.R.D.I.S, it stands for, Time and Relative Dimensions In Space.
The Doctor's So called Grandaughter Susan gave the craft that name in the first pilot episode of the show called " The Unearthly Child"
The Tardis is able to travel anywhere in the known and unknown universe, and visit any time period the Doctor wishes to go to.
She is a very rare Type-40 Tardis, they are very tempermental, that is why the Doctor is always having trouble piloting his craft.
The Tardis looks like a British police call box because it's cloaking devive got stuck on a previous misadventure to London. The cloaking device is called a "Chameleon Circut"
In the early 1900's call boxes like that were very common in London, they were used to summon police in times of danger, at some local colleges here in new mexico they have some type of blue tower devices used to call for help. Inside the box there would be a little door and there would be a phone inside, using the phone would also cause the blue light atop the box to start flashing, thus leading the police to the location.
The Doctor has grown to love her present shape, as do all the Doctor Who fans. It looks so out of place that it looks cool, nothing more beautiful than a spinning blue police box speeding through the time space vortex.
For all the Star Trek raised people out there, the time space vortex is also refered to as a "Worm Hole", although I prefer the term Time space vortex myself.
The Tardis is able to freely travel thorough the universe, through time and space and also into various different dimensions, it is even capable of going into invidual cells of a body.
The Tardis and the Doctor are linked together by a psychic bond, and they are able to communicate telephatically.
The Tardis is basically a living being, not just an ordinary machine like the rather primative U.S.S Enterprise.
Below are some clickable links so you can see various parts of the T.A.R.D.I.S, and even get to hear the wonderful sounds she makes, the sound of her Dematerializing or materializing are unforgettable, I also love Her warning sound, the Cloister Bell chime, it's great.