Regicide

Once you have completed the Underground Pass Quest, at some point a Messenger will appear and give you a letter. Read it and speak to King Lathas in Ardougne. He will tell you that the way to the realm of the Elves is now open, and you must go through the Underground Pass to get there. Head to the pass which is located in the cave near Koftik in the western-most part of West Ardougne.

Once inside of the cave, you should see 3 paths. Don't take the middle one! Climb the rockslides to the north, and then you should see Koftik near a campfire. Take a few cloths from him and use them on your arrows, and then use the arrows on the fire to get Fire Arrows. Head north and shoot the rope holding the bridge up.

Now head south, and then east along the path until you come across a big hole with a pole rock on the ceiling. Use your rope with it to climb across, and if you fail you'll need to cross the bottom again and restart the pass. Once you cross the obstacle you'll lose your rope.Keep following the path and then climb the rocks, where you'll then find the Grid Floors from the Underground Pass Quest. Remember that everyone's path is different, but yours will be the same as it was for the Underground Pass Quest.

After that, run through the hidden spikes corridor, climb down the well, go inside of the jail to the south, use your spade on the mud pile and then cross the ledge. You can either try crossing the bridges, or you could picklock the south gate if you have 50 Thieving. Cross the pipe and you'll end up in the Unicorn place. Proceed past the Paladins (don't speak to them or they will take you as one of the Iban Disciples), pass over the plank trap, and then open the doors. Head to Iban's Chamber where you defeated him before, go inside and then speak to Koftik, who may give you food. Then enter the Well of Voyage! Proceed out of the cave or recharge your Prayer and then continue.

Now that you're through the pass, you'll be in the Elves' Realm, which is in the west-most part of RuneScape. For a fully-featured map of the area, see the Map of Isafdar. Shortly after leaving the pass, you'll be greeted by an Elf, but he will get shot down by 2 others. They will tell you that Lord Iowerth is expecting you in his camp to the northwest. Remember, the lands may look peaceful, but they're full of traps, so watch you step! The map above will show you which trail to take to the camp.

There are 3 main kinds of traps you may come across:
Leaves Traps - appear to be bushes and trees, but by walking under them you'll be hit by a lot of damage. If you find 1, you can try to jump over it by selecting the "Jump Leaves" option.
Stick Traps - right-click these to try and cross over them, but if you fail, you'll take damage.
Trip Wire Traps - these are normally hidden between rocks, and they will poison you if you walk through them. Right-click them and choose the "step over" option to try and get past them.

Once you've found your way to the Elf Camp, speak with Lord Iowerth. He wants you to find his Tracker in the lands to the south. Head south until you find the Tracker, who thinks that you're one of Tyras' men. Go back to Iowerth to get a pendant to show to the Tracker again. He will tell you that Tyras' men have moved, and that you'll need to search for footprints to the west.

Once you've searched them, you'll be able to pass through Dense Forests. Cross through the nearby Dense Forest and you'll be attacked by Tyras' (level 110) Guard.Kill him and proceed, but be sure to watch out for Trip Wires!

Carefully walk to Tyras' Camp and speak to General Hinning. Pick up as many Barrels as you can hold, and if you have Limestone with you, grind it with your Pestle and then use it on the Furnace in the eastern part of the camp. You can also buy food and Halberds (Dragon isn't available until you finish the quest) from the General Store. After speaking to the General, head back to the Tracker.

Talk with him, and while you're there, use your Barrel with the swamp to the south to get a Coal-Tar Barrel, and then take some Sulphur and crush it with your Pestle. Go back to Lord Iowerth, and he will give you a Book O' Bangs with steps to making an explosive:
Sulphur - found south of the Tracker, must be crushed with a Pestle.
Quicklime - get some Limestone from the mine northeast of Varrock (on the way to Canifis) or northeast of Tyrannwyn. Use this with a furnace and then ground it up with a Pestle while holding a Pot.

Talk to the Chemist and then pour the Coal Tar into the Distiller on the table. Put some Coal inside and the heat will increase. When the heat level turns green, turn the right valve on. If the pressure goes over the green level, turn the left valve on. Don't let the pressure get too low, so be sure to close the valve when it goes below the green level. Do this until the Coal-Tar is distilled (the bar is completely green). Now add the ground Sulphur and Quicklime, and now you have a Barrel-O-Boom!

Get back to Ardougne and bring some food, your Bomb Barrel, 4 Balls of Wool, Bow and Arrows, Hatchet and Tinderbox, Spade, Rope, money to buy a Halberd, and Antipoison Potions. You don't need any armor here.

Go through the Underground Pass again, go to the Elf Camp and use your 4 Balls of Wool with the Loom in the tent west of Iowerth to make a Cloth, and then use it on the Barrel. Go to the Catapult near Tyras' Camp, talk with the Guard and give him some Cooked Rabbit. Quickly use the Catapult and Tyras' Camp will be Destroyed!

Go into the camp and try to enter Tyras' ex-tent. The guards are all saying that he's dead, and that they must prepare for the oncoming darkness. Talk to the Tracker on your way out, and then go back to Lord Iowerth to give him the news. He gives you a Scroll and access to the Arandar Gates leading to the Gnome Stronghold! Head back to the king by either teleporting or taking the gates.