The home of Asheron on Asheron's Island. Located at 21.1N, 69.3E on top of a huge mountain, with a long spiraling path up.
The castle has been playing a major role during the A Time of Chaos story arc. Since then, the Castle has been accessible on and off during different story arcs.
Now, the Castle and its NPCs play a major role in the Quiddity Seed quests.