Doctor Who: 14 Cool Details Revealed In Steven Moffat's Wedding Of River Song Commentary
4. The Pyramid Scenes Were Shot In The Same Place As Hitler's Office
Different episodes of Doctor Who are always using the same locations, and on top of the Calisto B steel mill, there's another example of this in The Wedding Of River Song.
According to Moffat and Webb, the pyramid set was also used as the "office of Hitler" in an earlier Series 6 episode, Let's Kill Hitler.
These two episodes were shot back-to-back (and they have lots of crossover locations, like the scenes inside the Teselecta), which likely made it easier to re-dress this room and use it for a radically different scene.