On 15 November 2009, millions of people settled in for a special episode of Doctor Who.
David Tennant's Tenth Doctor would travel to a human colony on Mars, where he would meet Captain Adelaide Brooke and her crew. Unfortunately, they were not alone on the red planet, as a deadly parasite living in the water was about to make itself known.
This was The Waters of Mars.
Written by Russell T Davies and Phil Ford, The Waters of Mars served as a vital turning point in Tennant's time on the show. After being warned of his impending death in the previous special, he became reckless and broke the laws of time, setting up his eventual demise in the following two-parter, The End of Time.
So, quite a big episode then, and where there's a big episode of Doctor Who, there's plenty of behind-the-scenes trivia to get stuck into.
From the episode's original title to callbacks to episodes from Who's distant past, this list is about to flood your brain with tons of cool information you likely didn't know about The Waters of Mars...
20. It Was Almost Set In A Hotel
Remember the Series 6 episode The God Complex, the one set in the hotel with the minotaur and David Walliams? Well, this is almost what The Waters of Mars ended up looking like. Sort of.
Russell T Davies' original plan for the episode was to revive an idea he'd had where the Doctor would travel to a strange hotel that had somehow caused Earth to be frozen in time.
Unfortunately, RTD soon realised that his vision of the Doctor exploring an abandoned London would cost a lot of money, and would be very complicated to pull off.
The hotel idea was shelved, and Steven Moffat and Toby Whithouse developed a totally different hotel idea a few years later.