According to director Melanie Anne Phillips the opening scene was shot without permission at a real mine called "The Red Rover". About a month after shooting their scenes some real life miners hired to see if the mine was worth reopening entered and went further in than the film crew had, then died from poison gas exposure.
Chris Huntley, who designed and built the models used for the creature the crew would affectionately come to refer to as "Binky", swears its obvious resemblance to a vagina was completely unintentional.
A sizable number of the underground cave scenes were shot on a set built in director Melanie Anne Phillips's grandparents' garage.
The stop-motion animation monster was nicknamed Binky by the filmmakers.