"As you walked up from the harbour, you probably noticed two things. First, the castle is set in the side of a mountain. Second, its walls have a rather strange shape."
"...The layout is pentagonal. The reason is simple. It is an architectural approximation of the crown of Amber. Oh yes, those globes atop the corners? They're magical. If you don't believe me, try besieging the place. Trust me: you'll never get through."
(The Visual Guide to Castle Amber)
Well, who could trust the word of an Amberite? The Castle fell, though not through any weakness of its walls. If it were fully garrisoned and defended by its liege, the castle of Amber would be impregnable even against the winged legions of Chaos. To the despair of the citizens, the gates were opened without a shot being fired in anger as the royal family had already been scattered and their cause left in tatters on the Field of Tears.
The stone and slate owe no allegiance, and serve their Chaosian masters as well as they served the descendants of the Unicorn. It is rumoured to have many secrets within, that the residents have never truly investigated. The miles of tunnels beneath the castle, the mystic Hall of Mirrors, the bedrooms and corridors stalked by the phantoms of long-dead princes. It is this unnatural quality that lends bards to tell that the children of the Unicorn can enter the castle at will, and the Lords of Chaos know nothing about the rebel lords stalking the halls of their forefathers. Certainly, the new masters have kept many of the old retainers, finding it hard to convince Lords of Chaos to stay any longer than necessary. All except Mandor, of course, who sits as though the King's throne were his own.
Certain Rooms and Areas with Castle Amber