Upon zoning into Castle Zvahl Baileys , go straight until you encounter the first intersection and make a left. Go down a small flight of stairs and then turn right and follow the left wall and you will enter the Orc section of the castle.
Go through the area to the west again and eventually you will zone into Castle Zvahl Keep.
Once you enter Castle Zvahl Keep, you will have to open several gates, very often in front of mobs that detect on sight.
You will encounter a series of teleport devices. These devices will cancel the Invisible effect after they are used. Once you use the last device, run to the west exit of the map where you will find a zoneline to the Throne Room.
When ready, gather in front of the door. When you enter, a cutscene will happen and the fight begins. Cast the prefight buffs before getting closer.