5Z2 - Castrovalva 2

Only twice has Doctor Who attempted to explore the vastness of the dimensions inside the TARDIS - once in The Invasion of Time, and again in Castrovalva. The latter was the more successful of the attempts, as instead of abandoned hospital corridors doubling as the various hallways inside the ship, in Castrovalva, these scenes are shot in the studio with actual sets - roundels and all.

And at this rate, one better enjoy the TARDIS while we still can, because Christopher H. Bidmead must really hate it. After forcing The Doctor to jettison Romana's room in order to get out of a tricky situation in Logopolis, in Castrovalva, The Doctor calculates that the only way to drop enough ballast to escape the hydrogen inrush is to drop a whopping 25% of the infrastructure. What's going to be left of the ship?

Only towards the very end of this episode are more characters introduced into the story (albeit briefly) as the TARDIS finally lands on Castrovalva. To have only five characters carry the entire first half of a story in the 1980s television environment is a bold move, but it's been an entertaining one, and has actually justified what will soon become a superfluous number of companions.