Once you have the ULU-MULU head back into the Orc Territories towards the Orc city. On your way there you'll find Ur-Shak near the city. He says that there are two ways to enter the Sleeper's temple. The first way is to use a teleport spell you will find in the Shaman's chests, but Orcs hate magic and will attack you if you use it. The other way is to climb the Sleeper's statue and there's some kind of switch there (note: you need to change into a bloodfly and fly onto one of the nearby "outer pillars" near the statue. It can be awkward to do, but it can be done. Then, change back into human form while on the small "outer pillar" and use telekinesis spell to acquire the object on top of the main "statue pillar". This statue object then works with the switch to allow access).
He'll also tell you that you need to have the ULU-MULU in hand when you cross the bridge, but it works while sheathed too. If you draw your ULU-MULU (it's a weapon really) the Orcs will say to put the weapon away, only in Orcish. Walk around and find four Orc Shamans kneeling before the Sleeper's statue. Nearby are some caves. Go in each one and take what's in the chests. One of them should give you an Orc Teleport scroll. Use it and you'll find yourself at the other side of the gate. Continue forward into the Sleeper's temple. . Once you're on the other side of the gate, if you go near the gate the Orc Shamans will start fireballing you through the gate, but you can easily dodge out of the way. The other way of getting past the gate is to climb the statue or use telekinesis to obtain the figurine on top and use it on the switch next to the gate, but teleporting is easier.
Once inside, a new journal entry will be added. This is the first time it does so without talking with someone. Keep going until you see a big entrance with the largest pitfall in front of it you'll likey ever have seen in a game (you'll fall for ten seconds, and considering how fast you go when you fall, ten seconds is a lot). Luckily there's a pillar fallen over you can walk across. Once inside, you'll fight some skeletons. The warriors are the biggest threat to you since they have the best weapons. Kill them first, as the scouts and the regular skeletons aren't going to hurt you that bad. You will also come across two or three skeleton mages inside the temple. They summon three extra skeletons to fight with you, so go after the mages as soon as you can so you save yourself a headache later.
You should be in a big room now, with three barred gates (one is down a ramp) and an open door. Don't go in yet; go in between the two gates that are closed and there's a stone block with some symbols. Remember the color pattern. Now go in the open gate back in the main room. You will come across a small hall. The door behind you will close and two skeletons are released from the cells to fight you. Kill them and collect some potions and random items in one of the cells. Look for a switch in both cells to open the gate in front of you. Now you see a big pillar in front of you. Go the sides and look for the colors that you were supposed to memorize. Go the proper color's switch and turn the switches in order. The three gates will open, and now you have access to the next part of the temple.
In the next room there will be a door on your left that leads into a hall. At the end of the hall, turn the switch on the left. The gate inside of the minecrawler tunnel will open, some platforms will lower and the door that leads to Varrag Hashor will open.
Go through the minecrawler tunnel that was previously blocked by the gate and you'll see Gothic/NPCs#TPL_1455_GORBOBA in front of a locked gate. Either off him or stay away as he won't attack you until you come close, and after opening the gate you could run past him. Left of Gor Boba there's a room that's painted red in an interesting way, and clearly not by Bob Ross. It's blood, that should have been your first warning. In the room there is a button near the ceiling. Make sure you are standing outside the room (you'll understand soon enough) as you fire an arrow at that button. Enter the room again and use a torch or light spell. A part of the wall will lower. Fire an arrow at the revealed wall button. Remember the order of the colors. The gates of another room will open. In that room, turn the switches in the order of the colors. If you turn them in the wrong order, you can gain infinite experience. Now the gate that Gor Boba is guarding will open.
Go through the gate he's guarding and turn right. Cross the minecrawler chasm. On the other side, you'll find a box. It will highlight, but it doesn't have a name, similar to benches. Open it to find a ring of greater invincibility and an essence of strength potion. (+3 strength)
When you reach the lava lake with the platform in it that has a switch on top, turn that switch. You'll go down and find yourself in a room with two switches. Use a torch or light spell to see what they do. The one on the left will open just the gate you need, the one on the right will also open the gate for a room with additional loot (an axe and some potions), but also spawn some more monsters. If you opened the gates for the extra loot, the room on the right has an elixer of healing and a healing scroll. However, there are also some potions stuck on the wall. If you use telekinesis on them, they will fall down. Be careful though, they can fall through the floor. On the wall, you'll find an elixer of magic energy (mana bonus +70) and two elixers of life. (maximum life +15 each)
You can now visit all five of the undead orc priests. But you probably shouldn't.. yet. Go to Varrag Ruushk and use telekinesis to get the Strange Sword. (or take on Varrag Ruushk) Once you have the Strange Sword, you can leave the temple and teleport to Xardas. (you must be back in the main world to teleport) Now do The Magic Sword URIZIEL as you'll get a better weapon and armor which will make it easier to take on the orc priests. In addition, you'll need this to take on Vrash Harrag Arushnat.
Varrag Hashor
Varrag Hashor will fight you with Pyrokinesis.
Varrag Kasorg
When you go right at the split in the minecrawler tunnel, you'll find three rooms with switches. After turning them, Varrag Kasorg will appear (along with some other monsters) who will attack you with Ball Lightning.
Varrag Ruushk
Varrag Ruushk will attack you with Storm of Fire. Also, he's guarding the Strange Sword. He's in a building that is surrounded by a moat filled with lava. Around this there are three rooms that each have a switch in them. Turn them to access the bridge across the moat. Walk over the bridge, but don't enter the building. (unless you like satay) Go right of it and climb into the hole in the wall. You can now either go in and take on Varrag Ruushk, or use telekinesis to get the Strange Sword without a fight.
Varrag Unhilqt
Varrag Unhilqt will attack you with Chain Lightning.
Vrash Harrag Arushnat
Vrash Harrag Arushnat is the final orc priest who will attack you with Breath of Death, but when you try and attack him, Nameless will directly comment on his weapons being of no use against this orc priest. Make sure you did aquire the Strange Sword, leave the sleeper temple and once outside, teleport back to the Necromancer.