This TV series largely exists nowadays as a set of black-and-white film recordings. The color video tape copy was lost many years ago at a time when it was common to reuse video tape once it had been broadcast; this said the vast majority of episode 6 still survives on colour videotape.
In Clearwell Caves, where the caving scenes were filmed, there is a small plaque that describes a ghostly event which occurred during filming. A lighting technician found that a cable was not long enough to reach underground. He turned and found an old man who told him about a shorter passage which allowed the available cable to be used. But when he turned to thank the man he had gone, and no-one else in the cave knew who he was. When everyone was counted out of the caves at the end of the day's filming, the old man was not amongst them. The staff told the film crew that other people had reported seeing the old man over the years.
Some crew members were only credited for a few episodes, even though it is highly likely that they worked on the whole series of 13 episodes. The graphics designer was only credited for episodes 1.1, 1.2, 1.3 and 1.4, and the cameraman, sound recordist and editor were only credited for 1.4, 1.11 and 1.12.