The Legend of Prince Valiant - Season 2 Episode 34 A Light in the Dark

Valiant is directly advised against returning to Camelot via a dangerous route through the Great Swamp. But the prince is far too curious about the ""great evil"" that lives there to pass up the chance to investigate. Arn and Rowanne soon wish he had heeded the warning as they are all attacked by creatures out of a nightmare. In fact, that's just where they've landed themselves - in a nightmare world that is controlled by an old enemy.