Castle Alderweg is a mythical fortress which, according to the legends, is unassailable. Supposedly, at some point in history, an artifact called the Gauntlet was created to destroy the fortress. In response, an artifact known as the Sentinel was created to counter it.
No one really knows where Castle Alderweg is (assuming it actually exists). Supposedly, the fortress impedes the progress of evil on a mass scale, but it’s unclear from the legends what that really means. Most people assume that Castle Alderweg exists out in the Glass Wastes and that it stopped, long ago, some horror from coming from the north. If that’s so, the villa in the Reach Highlands was pretty damn far away from the Family Van Artog’s last known post.