Annuvin was a wasteland of dark enchantment, and its very environment was deadly for most living things, especially Fair Folk. The closest Fair Folk way post to Annuvin was that run by Gwystyl; such near proximity to the Land of Death seemed to affect his health and temperament for the worst. Doli himself found that Fair Folk who lingered inside the borders of Annuvin would weaken and die -- until the dwarf discovered that when invisible he was immune to the effect.Ruler of Annuvin, one must wrest power from the current ruler, or the Iron Crown will burn one to death when placed on the would-be usurper's head. Magg made that very mistake near the climax of The High King. Dyrnwyn from the Sons of Don.
The former Queen of Annuvin, Achren, was the only one who knew the paths over the mountain — even Arawn did not have complete knowledge of its passes. When Taran's war band traveled it, Achren used her superior knowledge to give them an advantage over the Huntsmen of Annuvin.
A small peak jutted off of Mount Dragon. Once over the summit, the Iron Portals were a short distance down an unobstructed slope on the other side. The Hall of Warriors (where once stood the Black Crochan), and Arawn's Great Hall could be seen from that vantage point.The Black Cauldron, the war party of the Sons of Don used this entrance when they attempted to seize the Black Crochan. It was a shorter route but more dangerous to traverse, and thus not as heavily guarded as other entrances to Annuvin.
The Forbidden Forest
The Forbidden Forest is a small forest surrounding the east side of the massive Horned King's castle. Taran loses track of Hen Wen here while daydreaming about becoming a great warrior, and along the way meets Gurgi. The gwythaints capture Hen Wen and carry her over a deep thicket and tall mountain into the Horned King's castle. The Sierra game reveals that Gwystyl lives on the other side of this dark forest.
A large moat surrounds the castle. The moat possibly contains alligators; part of it is certainly poisonous. In the movie, Taran is able to drop Hen Wen into a non-lethal section during his first attempted escape. During the climax of the film, Taran, Eilonwy, and Fflewddur use a boat to escape from the collapsing castle. The trio watch the last remains explode from a safe distance.