Impenetrable Forest

"Everything in this forest... It's bewildering."

- Merlin to Queen Mab

The Impenetrable Forest is a desolate, nearly impassible forest barring the way to the Dark Tower. It is inhabited by vegetation dense enough to break swords and is guarded by a spirit called Queen Mab.

History
After Morgana kidnapped Gwen and imprisoned her in the Dark Tower, Merlin, Arthur, and the Knights of the Round Table were forced to fight their way through the forest to rescue her. They struggled to move through the dense foliage and later discovered they'd spent the day traveling in circles.

That night, Merlin was visited by Queen Mab, the spirit of the forest. Speaking in riddles and rhyme, Mab told Merlin to use his magic to navigate the forest and warned him that one of his party would not return. Merlin later used her advice to lead Arthur and the Knights out of the forest to the Dollares Plains (The Dark Tower).

Trivia

 * The forest may be enchanted, as Arthur was unable to navigate it with cardinal directions and wandered in circles until Merlin used his magic to visualize the path ahead (The Dark Tower).