As contemporary Cardiff, location of the "Doctor Who" production, did not have enough Victorian architecture, the episode was filmed in Swansea, and computer generated imagery (CGI) was used as the main visual effect for the Gelth.
The episode was filmed in Swansea. Contemporary Cardiff did not have enough Victorian architecture. Contemporary Cardiff were location of the "Doctor Who" production. Computer generated. Imagery (CGI) was used as the main visual effect for the Gelth.