The Citadel is the home/base of the Inquisitors. They are a group of particulary violent soldiers who hate magic and anyone who uses it. There are 4 types of Inquisitors: guards, captains, crusaders, and the Grand Inquisitor himself. If you walk by any Inquisitors they will attack you for no reason. In the beginning there is a poor old mage/wizard named Murry who was captured and "tortured" by the Inquisitors. Such types of tortue included slapping him with fish and suspending him upside-down in buckets of Horc sweat. There is also a passage in the cave where you need 50 bone dusts to get past. Bone dusts are found in any skeletons/undead. There is also a Mana-sucking creature called Belrot the Fiend who is guarding the Grand Inquisitor. You must deafeat him before going on. The long path (with guards all over it) leads to the GI's castle. You can see the castle in the background in the pic below.