When Doctor Who debuted in 1963 before you even saw William Hartnell step out as the First Doctor you saw the blue police telephone box that we all know as the Tardis. The time machine and space ship is The Doctor's constant companion in his adventures, appearing in nearly all of them across television, prose, comics, games and audio plays.
And yet, for as many times as we see it there are still hidden bits of knowledge about The Doctor's Tardis that remain fairly uncommon knowledge. For instance did you know...
The BBC Actually Owns the Trademark on Police Boxes One of the points of the Tardis's police box appearance is that it was appropriate camouflage for 1963 London because public call boxes were a common sight (Fun extra fact; the concept of the police box is actually an American one, though it was perfected and more popular when exported to Britain.) So you'd think if anyone owns the trademark on the police box it would be, well, the police, right? They probably lend it to the BBC or something.
Sort of and no. The Metropolitan Police originally gave the BBC permission to use the image, though a 1998 lawsuit said that they never relinquished their trademark. The lawsuit was a result of the BBC trademarking images of the police box for all commercial use after the Trade Marks Act 1994. The police sued saying that the box was obviously more associated with them than Doctor Who, but the courts decided that because of the current scarcity of the boxes still in use — fewer than 100 in Britain at the time — the opposite was true. Also, the police had not created the look of the box in any case.
So not only did the BBC now own the trademark, the courts even ordered the police to pay for the law suit's court costs, £800 ($1,716.49 in today's dollars at the current exchange rate). The lesson here is, do not sue the BBC. Speaking of the police box shape...
The Chameleon Circuit Is Sabotaged, Not Broken Show lore holds that Tardises are supposed to blend into their surroundings, and other Tardises that have appeared do, such as The Master's and The Meddling Monk's. The Doctor's Tardis, however, has a broken circuit that locked into the shape of a police box when the First Doctor left Earth in 1963 with Ian, Barbara and Susan. Upon arriving in Earth's prehistory he asks why it had not changed. In the comic story Hunters of the Burning Stone though it's shown that the circuit was deliberately sabotaged by the Eleventh Doctor on a trip to 1963. He wished to have the image appear throughout Earth's history so that people would recognize it as a source of help.
How Big is The Tardis? The massive size of the Tardis's interior has been hinted at a number of times. The Twelfth Doctor remarked that if he used the ship's actual mass in a landing the Earth would crack, and on Trenzalore the Doctor's grave is housed inside his Tardis leaking dimensionally and growing ever larger. However, the proper interior size of the Tardis has only manifested itself as the exterior once, in the Eighth Doctor novel The Ancestor Cell. After being infected with a virus the Tardis appears over Gallifrey as a giant six-petaled flower, a symbol of death used in Time Lord funerals. It is so big that it cannot be seen fully with just eyesight from the planet and has to be viewed fourth-dimensionally. According to science, Gallifrey is roughly 250 percent the size of Earth, so an object that dwarfed Gallifrey itself would like put the full size of the Tardis somewhere around that of the planet Neptune or beyond. That's a lot of corridors.
The Tardis Has at Least Two Back Doors The front doors aren't the only way into the Tardis. The Second Doctor particularly was prone to getting locked out and needing a new way to get in. In the comic Peril at 60 Fathoms he entered by lifting a panel on the roof, and in the novel Heart of Tardis he tried several back panels that were usually back doors as well as a cat flap. Leela at some point also discovered the back door to the Tardis, something that even Romana didn't know.
The Location of the Wardrobe is Directly Related to The Doctor's Style One of the few rooms that is pretty regularly shown besides the console room is The Doctor's wardrobe, however its location in relation to the control room shifts dramatically between Doctors seemingly based on their sense of style. During the time of the Fifth, Sixth and Seventh Doctors for example the wardrobe was quite close to the console room, reflecting the colorful nature of the three Doctors' dress sense. The Ninth Doctor, known for his drab style and reticence for foppishness, has to give Rose intricate directions to reach the wardrobe, whereas the Eleventh Doctor gives River a less complicated set indicating it's closer because he likes to dress up more.
Idris is Not The Only Time The Tardis Has Assumed Human Form "The Doctor's Wife" is easily one of the most beloved episodes of the show, following the adventures of The Doctor outside the universe where the sinister House drains the Tardis of its energy and imprints it into a woman named Idris to die so he can inhabit the shell of the Tardis himself. This gives The Doctor and the Tardis the unique chance to talk out loud for the first time and reveals much about the ship's sentience.
Except that it isn't the first time. During the Eighth Doctor's battles with Zagreus the Tardis takes on the form of Brigadier Alistair Gordon Lethbridge-Stewart, seemingly betraying The Doctor to ally with Rassilon but secretly trying to save The Doctor by guiding Charley Pollard through the ruined and badly-damaged interior of the ship. The Eighth Doctor also journeys for a while with a sentient Tardis in human form named Compassion while his was seemingly destroyed and Rose Tyler arguably becomes a human avatar of the Tardis in her Bad Wolf incarnation, albeit temporarily.
The Doctor Stores All His Companions Old Rooms Exactly as They Left Every traveling companion who joins The Doctor on the Tardis gets his or her own room, but what does The Doctor do with those quarters once they leave? In the audio play "Relative Dimensions" Susan, Lucie Miller and The Doctor's grandson Alex discover that The Doctor keeps a holding ring of rooms available just in case any of them return to him, or perhaps out of a sense of nostalgia. He even has one prepared for Alex in hopes that he will join and perhaps one day inherit the Tardis. In the end though he deletes all but one of the rooms. His nostalgic streak isn't over, though. Popular fan rumor is that the Gallifreyan writing above the console is the names of everyone who has ever traveled with The Doctor.
The Library is Temporally Omnipresent Another of the rare rooms that's been featured on screen is the Tardis library filled with books from across time and space. It has a slight quirk in that it is actually the same library across all incarnations so that changing something in it changes it for all Doctors even if they precede the change from their perspective. This manifests itself mostly through the Eleventh Doctor's habit of ripping the final pages out of books so that the story is never over. Both the Tenth and the Eighth Doctors have complained about finding books with their last pages gone in the library even though technically it's their successor who actually ruins them and the ripping shouldn't have happened yet.
The Tardis Has a Birthday Originally The Doctor claimed to have built the Tardis but now admits that he actually stole it. Still, he apparently knows the date of its manufacturing because he celebrates the ship's "birthday" on occasion. In the novel Dark Horizons he describes taking the ship on a thrilling ride on the very edge of the universe as a birthday present, though he does not disclose the actual date.
It Has Never Been 100 Percent Established That The Tardis Has a Toilet Bathrooms and taking baths have been mentioned multiple times across media in Doctor Who, but the existence of a toilet on the Tardis has never been seen. It was rare to show bathrooms on television even through the 1970s (A toilet flushing was first heard on television in a 1971 All in the Family episode), so the classic show is largely excused but it's sort of weird that the revived show has been able to go through eight seasons without a single potty joke. In fact, the Eleventh Doctor dropping an Ood off at Amy and Rory's house where they find him on their toilet sort of implies that the Tardis doesn't have a toilet and has to make stops like on a car ride.
In fact, when you think about it randomly stopping to pee would kind of explain all the weird scenarios the Tardis seems to land in randomly.