Doctor Who
Castrovalva, Part Four
Season 19, Episode 4 · Aired 1982-01-12

Synopsis
The Doctor discovers Castrovalva is a cursive occlusion, an impossible yet manifested Escheresque environment, with all pathways, no matter which direction one goes, leading back to the same point. It is a trap laid by the Master with no apparent way out.
In the series
This episode is part of Doctor Who (1963–) on BBC.
A time-traveling renegade in a police box — regeneration as infinite franchise life.
Key cast
- William Hartnell as The First Doctor
- Patrick Troughton as The Second Doctor
- Jon Pertwee as The Third Doctor