The castle/fortress was the same one used in the Remake of Papillion as the last resort island aka Devils Island.
When playing Scylla the mermaid, Zorana Kostic Obradovic wore neither shirt nor bra in filming, giving her the ancient mermaids appearance, though her breasts were obscured by her hair. She also crawled around before her legs were digitally replaced by a mermaid tail in the final production.