The Castle that portrays Terror Tower in London is actually Casa Loma Castle located in Toronto, Canada. In the episode, it was supposedly built in medieval times. However, the real castle was constructed in 1914.
Kathryn Short (Sue) played Sabrina in the series premiere, "The Haunted Mask" and its sequel, "Haunted Mask II".
This episode is based on Goosebumps book #27.
The VHS release for The Haunted Mask features a behind the scenes sneak peek for A Night in Terror Tower, which was hosted by the episode's co-star, Corey Sevier.