Doctor Who: 20 Things You Didn't Know About Heaven Sent
4. The Castle Had Been Seen Before
Because constantly-changing castles don't exist in the real world, the Doctor Who team had to use regular old castles to film Heaven Sent in.
The two they chose - Caerphilly Castle and Cardiff Castle - had both appeared in Doctor Who before.
Caerphilly Castle was used as certain parts of the acid factory in The Rebel Flesh/The Almost People, and also for some of the underground tunnel scenes in The Vampires of Venice.
Cardiff Castle was also used in The Rebel Flesh, and was also seen in the Torchwood episode Exit Wounds.
Has any other show done more for Welsh tourism than Doctor Who?