In the land of Serkesh, you'll find a Miller walking around outside a mill, talk to him and he will tell you how his apprentice went down into the mill and hasn't returned.

Go down into the mill and you'll find yourself in a little room. Over to the left there's a teleportation pad, go through, but be ready to fight a few bats with a lot of hit points, I normally use invisibility before going through. Then over to the side there's a switch, go through the door that opens and you will find the missing apprentice. But when you talk to him you find out he was bitten by an angry vampire, and will soon be one himself. Kill him as soon as that happens, and then on the other side of the room he was standing in, there's another teleportation pad (not the one to go back to the previous room). Use the pad and then just follow along the corridor, kill the creatures there and go in yet another teleportation pad. Explore that section and eventually you will find a gate; the switch being over to the right with some spectres guarding it, a fair way from the actual gate. Through the gate you will need to kill 2 werewolves, destroy the crate next to the cauldron, and you will find the Rock Breaking Hammer.

Now go through the teleportation pad there, which will lead you back to the stairs leading to level 26, but don't go down yet, there's another teleportation pad there leading back to the starting room with the stairs going back to Serkesh. So return above ground and, if you haven't already, find a circle of trees with the entrance blocked by a large rock, and then just equip the Rock Breaking Hammer, break the rock and kill the rat man in there. He will drop The Vampires Sceptre, which you will need later on.

Now go back down to 25, through the teleportation pad, and down to level 26. Now, on levels 26 and 27 you will find 2 coffins, the first one containing Luxorious' Cape, and the second one containing Luxorious' Ring (though be careful opening the coffin on level 27, when you open it a few Skeletons Captains and 2 Vampires will appear, use reflection and you will be safe from the Skeleton Captains).

Then continue to down level 28 where you will find a door with a human guard, show him one of the items (sceptre, cape or ring) and you will be permitted to see his master, Luxorious. Walk down to the last room and give Luxorious all of his items; you will have to be fairly fast though, it's best not to listen to what he says, just press Exit each time and give him the next item, you can press H afterwards if you want to hear what he was going to say. Either that or don't bother giving them to him, which will cause him to attack you (if you do it this way you won't need his cape or ring, but you will still need the sceptre to get past the guard). You will get the Crystal of Strength both ways, either by Luxorious giving it to you in return for his items, or by him dropping it when you kill him.