Reaching Castle Barataria is your main goal for much of Ultima II. All you need to do here is speak to Father Antos, who can be found in Le Chapel. To get there, you can either use two Keys in the throne room and work your way south through a jail and a swamp, or you can Attack a Guard and try to get out before the rest reach you. You'll have to fight at least four Guards this way, so make sure you're well-equipped.
Also note that King Ozy (on the left) will raise your HP just like Lord British.
Also note that King Ozy (on the left) will raise your HP just like Lord British.