According to Brett Piper, a distributor said that if he wanted his movies to succeed overseas, they should have all action and no dialogue. Piper made this movie and showed it to the same distributor, who said "Geez, I can't sell this thing, there's no dialogue!"
Brett Piper said in a 2012 interview that the idea for the movie started when one of the actors he worked with in Mutant War (1988) asked if Piper would produce a film with him if he could raise the money. Piper agreed and they started batting around ideas. They finally settled on an old script Piper had written called Dark Sun, which they later changed to The Dark Fortress (later retitled again by Troma). Piper said he wanted to see if he could make a Ray Harryhausen-style period film with castles and monsters and costumes and such, but with very little money, and, of course, naked women. He thinks they succeeded, though the film doesn't hold up that well today, and they should have had more naked women.
Brett Piper be wrote a sequel Nymphoid II: Return to Dinosaur Hell and pitched it to Lloyd Kaufman at Troma. He seemed enthusiastic but it turned out he wanted Piper to raise the money himself, produce the film, and hand the finished product over to him, in return for which Piper would receive essentially nothing. So Piper passed.
The film was shot in Southern New Hampshire and northern Massachusetts because director Brett Piper lived on the border between the two, so it was closer to his home.
Troma was interested in distributing the film but they dragged out negotiations forever trying to nickel-and-dime director/producer Brett Piper to death. Eventually they came to an agreement and acquired the film. They then retitled the movie, shot a new opening, including the silly voice over, to justify the title. Piper said the style of the opening caused him a certain amount of trouble because people criticized the inconsistencies in the story, not knowing or caring, that it was never supposed to be a post-nuke tale like other Troma movies.