When Rose emerges from the Tardis after Torchwood moves it, the Egyptian Sarcophagus it's parked aside, is from Pyramids of Mars: Part One (1975), where it served as the Osirian Time-Space Tunnel conduit.
First usage of The Tenth Doctor's catchphrase "Allons-y".
Russell T. Davies had originally intended for Torchwood to be based in Cardiff, on the time rift, as had been introduced in The Unquiet Dead (2005). However, for this episode's plot structure, Torchwood is based at Canary Wharf, in London, but, when Torchwood (2006) went to series, Davies took the opportunity to base them back in Cardiff, Wales.
To ensure that Noel Clarke and Shaun Dingwall (Mickey Smith and Pete Tyler, respectively) were available for filming, the story was filmed in the season's third production block along with Rise of the Cybermen (2006) and The Age of Steel (2006).