The Underground Pass Quest

Start:
Get out king Lathas amulet and go talk to Lathas. He will tell you that the scouts have located the pass to the west of west Adrounge. You can enter the plague city by using the main gate now, do so. Head west, there is a general store on the way that sells food and other items useful in the quest. Eventually you will reach a cave opening with Koftik, the Kings chief tracker, outside it. Chat with him and enter the cave.

The Antechamber to the bridge:
The first thing you will see is that you are in a large chamber which proceeds to the west. Across the center is a green area with 'Swamp' tiles. On of the options is 'step over'. Do not do this, if you do, you will be sucked down and thrown down a slope and injured fairly badly and make no progress. Look to the north and south walls and you should see Rocks one of the options is Climb Over, do so. Now you will be in a narrow passage with more Rocks and Ledges which you need to climb. If you fail on rocks or ledges you'll lose a little hp, but not much. Eventually you will enter a small chamber, to the east is the antechamber, to the west is a river with a drawn up draw bridge on the far side. Koftik will also be in the chamber, you need to talk to him. He should give you a 'damp cloth' which if you examine will see it has been doused in alcohol. Use the cloth on an arrow, then use the arrow on the fire in the room to make a flaming 'lit arrow'. Now look for a pile of rocks farthest north and west, climb over it. You will immediately see a ledge, climb up it, and over another pile of rocks. You will now be on a sort of cliff overhanging the river, USE the arrow and select the “Old Bridge”, you don't need to equip anything, just have a bow with you. Depending on your ranged, bow, and arrows, you may or may not hit the bridge's rope and cause it to lower. If you miss, you must climb down and get another cloth from Koftik and repeat the process. If you hit the bridge, you will atomically cross.

Across the bridge:
This area has a lot of level 35 blessed spiders which seem non-aggressive and level 13 goblins. Look around for a mine-able rock, mining it will give you several large pieces of rock. Now head south-east to another large swamp, again, don't try to cross it. Instead, use the rocks with one of the swamp tiles near you. If they sink, you will need to mine more rocks. If they don't, you will automatically cross. There is another rock on the far side so don't worry about getting out. Now proceed east until you see a passage with another set of rocks, one of the options is 'clear', don't do that, it's a trap. Use the rope on an overhanging stalactite and you will climb up and cross safely, you retain the rope. Now you must follow a narrow passage until you reach a wide chamber with several Grills as the floor, many of these are traps. Look for another set of rocks, this one has no options, it's just the starting point. Now, from there head West onto the grills, west again, south, west, west, south, south, west. Pull the lever and the big gate you're at will open and you'll move on.

The four Orbs of light:
You will now be in a narrow passage heading west, with 3 searchable piles of rocks. Which are really traps, of course. Disarming them will let you into a small chamber with some Zombies, a furnace, a west and a north passage, and two plank spawns. Pick up the planks and go down the passage, which is a duplicate of the first one. You will now be in a chamber with an Alter to Zamorak, four more passages, a strange well, and a journal spawn. There's one north heading passage, one north-west, one south-west, and one directly west. As well as another plank spawn.
THE WHITE ORB: is down the single northern passage. Which is obviously trapped. Use a plank on the passage to go through, grab the orb, and use the other plank to come back. Grab another plank if you have 50+ thieving.
THE PURPLE ORB: is down the north-west passage and is simply guarded by three level 58 ogres.
THE BLUE ORB: is down the straight-west passage, there are about SIX traps which you must disarm. Failing can mean you'll get hit by each one until you're pushed out of the passage completely. This is very hard, clicking rapidly when you fail can keep you from getting pushed out all the way. I don't know if it has any bearing, but I searched each one rapidly and got through.
THE YELLOW ORB: is down the final south-west passage and you'll need to be pretty much healed to attempt it. Going into the passage causes it to tip up and turn into a spike pit, you need to grab the orb and try to climb out. This is very difficult and you could get killed if you're not careful. You might need to just teleport out if you're really stuck.
Now, take the four orbs back east to the furnace and put them in to destroy them. You can now climb down the well.

Down the well:
You'll be in a sort of wide passage with Koftik, who will talk to you, and a crate with food in it. Proceed west until you find a number of cages with slaves in them. Pick-lock the first one on the north side, search the dug up dirt inside, it will ask if you want to go through the cave you find inside, select yes and follow the cave to a 'wall grill', use the rope on it and go back to the slave-chamber. Head west until the passage ends at a ledge, don't jump off. Click on the wall grill instead and you'll grab the rope you tied there, climb up, and across. You'll now see a east and a south passage. If you have thieving over fifty you should go south, otherwise you must go east. The eastern passage has a chamber of narrow walkways and spike pits all around. Numerous 'rocks: Jump over' will block your way. If you fail you'll fall in the spikes and have to climb out somewhere further back. The southern passages quickly turns to run parallel to the eastern one, first you will encounter railing which you lock-pick, then a whole bunch of rats and bats, then more railing, another trapped passage (use the plank from the well-room on it), and finally one more railing. You'll enter a sort of wide passage which will turn back west. Also in the passage is another railing you can pick-lock and get a wormhole. At the end of the passage are some ledges which you must climb, this will take you to the unicorn cage chamber.

The unicorn:
In order to continue, you have to, I'm sorry to say, smash the unicorn flat as a pancake. The unicorn room has two ledges, one to the west and one along the south wall, and a unicorn behind some railing which you can't pick lock, search it to find a railing that has fallen off the cage. Now climb up the southern ledge, you'll be in a chamber sort of above the unicorn. In the South-east corner is a large boulder, use the spare railing you picked up to displace the boulder and squish the unicorn. Climb back down and search the cave remains for a damaged unicorn horn. Its exactly like a normal one except its examine is some like 'Poor unicorn went splat!'. You can drop the railing and climb out the western ledge.

The gate of Iban:
You'll be in another chamber with guess-who, Koftik who will sound pretty delirious. Keep going until you reach another pick-lock-able railing with several Zombies and 'Undead One's behind it, this can get a little dicey for low-combat leveled people, its hard to get through the chamber because of all the zombies in the way and the Undead Ones attacking you. But at the end is another railing with the 'pick lock' option, go through it and follow the passage to a chamber with three paladins. If you talk to the bearded paladin he'll give you some food and potions. Unfortunately, you apparently have to kill three of them to get the 'Coat of arms'. You need three to open Iban's Gate, when you kill one of the Paladins you automatically search its body and find a Coat of Arms. Proceed out of western passage, look out for more trapped rocks. Keep going until you see the 'Flames of Zamorak'. Throw in the Coats of Arms and the Horn. Congratulations! You're now evil enough to pass through the gate of Iban!

The doll:
Inside you'll find a series of stone platforms connected by, occasionally collapsed, bridges. Either try to take the stairs, or jump across the bridge in front of you. Either way you'll end up in a BIG chamber with Koftik who's completely lost it. He tells you about some dwarves in the south, go see them. This chamber if full of level 28 soulless, some spiders, bats and so forth. Talk to Niloof and Klank who will tell you about a witch, Karadia, who recalled Iban from the dead. Look along the south wall until you find a ladder, go up it. Now head North-east until you see a sort of little house, this is where the witch lives. Look through the railings on one of the walls and listen to what she says. She's lost her cat! Head north-west and keep an eye out for the cat. Once you find the it, take it back to Karadia's house and use it on the door. Then you can go in without getting shot by here spells. In the house is a chest, in the chest are some potions, a book, and a doll. Take them to the dwarves, read the book.

The four elements:
The book will tell you that there are four elements, flesh, blood, shadow, and conscience used to produce the doll that brought Iban to life, and that repeating the process will kill him. Go figure. Talk to Klank who will give you gauntlets and a tinderbox, which are both needed to get the items.
THE FLESH: go to the tomb of Iban, don't open it or his claws will come up and hit you. Ow! First get a bucket, then talk right-click the barrel behind the drunk dwarf that offeres you some of their brew. One of the options is 'Empty', select it and you'll fill the bucket with the Dwarves' brew. Use a bucket full of dwarf brew on the tomb, then use the tinderbox on it instead, it will turn to a fire, which automatically search and take ashes and that you must use on the doll.
THE BLOOD: head north again, you'll see an enclosed area accessed by a pick-lock-able railing. Enter and look for the really big level 78 spider, kill it and you'll automatically take some blood and wipe it on the doll. One of the blessed spiders will attack you after that, so look out if the big one lowered you HP very much.
THE SHADOW: this one is a little tougher. Go back up the ladder and head south as best you can. Eventually you should see a chest on a plotform, and three platforms with demons. You have to jump over or cross a broken bridge to get there. Kill the three demons (two level 78, one level 98,) . You'll automatically take their amulets. Now you can open the chest and get out the dark liquid that is Iban's shadow. Use it on the doll and leave that area.
THE CONSCIENCE: put on Klank's gauntlets. Go back down the stairs and head north along the west wall. You'll see a weird twisty little set of walls made from fence or railing. At the end is a pile of mud you can climb to get out onto the platforms. Head west along the bridges as far north as possible, you'll see a bunch of cages with soulless in them. When you get to the last one along the north, you'll see a partially collapsed bridge, cross it. Now head to the cage farthest south without crossing anymore collapsed or broken bridges. Search it and you'll find the dead dove. Use it on the doll. You have completed the doll!

The end:
If you have plenty of food, head south-east. Look for 'Temple of Zamorak' and Iban disciples. This is near the center of the platforms and you'll have to cross some broken bridges. If you have robes of Zamorak, put them on. If you don't, kills some disciples until they drop them. Either way, you have to be wearing them to enter the temple. Iban will say some stuff and shoot at you which does moderate damage. Apparently, running along one of the walls keeps you from getting hit. This is very confusing and can be rather dangerous. You need to throw (use) the doll on the 'Pit of the damned'. After that, Iban will stop shooting, say some more things about falling into darkness. Then the temple will collapse and you'll end up in a small cavern with Koftik who has recovered his senses and lead you out of the cave. Go talk to king Lathas.