1. The TARDIS is the Doctor’s irreplaceable time machine; the letters stand for Time And Relative Dimension In Space. (Acronyms rock.)
2. It looks like a blue police box, mainly due to a problem with its “chameleon circuit” which occurred in the very first episode, leaving it stuck with this appearance from then on. (And thank goodness for that faulty chameleon circuit!)
3. It is, famously, bigger on the inside than on the outside.
4. The TARDIS’s consciousness took on human form in the wonderful “The Doctor’s Wife” episode, revealing among other things that though she may not always take the Doctor where he wants to go, she always takes him where he NEEDS to go. (Take that, all you GPSes out there!)
5. The Doctor usually opens the doors of the TARDIS inward, although real police boxes open outward. (In “The Doctor’s Wife” episode, the TARDIS complains about the Doctor’s always opening the doors the wrong way.)
6. The shape and kind of key used to open the TARDIS has varied over the years; currently, it is a Yale lock key. (Hmmmm….I have a number of Yale lock keys myself….)
7. In addition to the oft-scene console room, the TARDIS contains a library, a swimming pool, sleeping quarters (initially with bunk beds for Amy and Rory, subsequently replaced with a regular bed), a scullery, a squash court and God only knows what else.
8. Other TARDISes have been seen over the course of the show – but because they had working chameleon circuits, they did not look like the Doctor’s TARDIS. (Sure, they have working chameleon circuits – but does that mean they have as much fun?)
9. An asteroid discovered in 1984 is named after the TARDIS.
10. According to River Song, the distinctive whirring sound that the TARDIS makes as it materializes or dematerializes is caused by the Doctor always leaving the brake on. (Don’t argue with The Song.)
(BTW – The new season of Doctor Who premieres on BBC America this Saturday!)