This is an old keep, one of the easter-most outposts of the Kingdom of Thaentis. A garrison of the kings guard stays there and is a minor hub of travel between the Thaentis and the Realm of Dusnain, who use it's Drochaid Stone (which sits inside the Citadel) for travel to major cities before fanning out locally.
Many trappers and farmers alike travel to the citadel to sell their goods and trade for exotic things from far distant regions, though they seldom stay more than a few days.