The cave scenes were filmed in Wookey Hole, near Wells. This was the same location used for the 1975 Doctor Who (1963) serial "Revenge of the Cybermen", also directed by Michael E. Briant.
Glynis Barber, who appears as the principal Mutoid in this episode, later returned to the show in the fourth season in the regular role of Soolin.
Glynis Barber was doubled by Stuart Fell in the scene where her mutoid leaps from a ledge and attacks a guard, who was doubled by Cyd Child. They originally planned to do the opposite stunts, but it didn't look right.
In the original script, Cally accompanied Blake to the planet. When Sally Knyvette complained that she wasn't given much to do, it was rewritten to have Jenna go down.