Crossroad Keep (Neverwinter Nights 2)
After defeating one of the primary villains in Act II you're rewarded with your very own ramshackle castle that's little more than a ruined fort.
Repairing the fortifications, building up the castle and attracting merchants to set up shop becomes an interesting and enjoyable ongoing side quest to your usual adventuring. Crossroad Keep may very well be the prototype for Dragon Age: Inquisition's Skyhold.
