Outside shots of Kaddal's monastery are actually of St. George's monastery in Wady Kelt, a gorge not far from Jericho in what is today the Palestinian Authority. In the time of filming, this area belonged to Israel. The underground caverns, allegedly under the fort, are in fact located more than a hundred km to the north east, in the Beit Guvrin national park, Israel.
Irving Kaplan, who plays Michael Rolands, is actually one of the founding members of Israeli Educational TV. He directed and participated in many popular programs during 70s and 80s, which are considered by many to be nostalgic gems.