Speak to Dondakan and ask him why he is firing his cannon at a wall. He will explain to you that he believes there are valuable minerals inside the rock, and enlists your help. The first thing he asks you to do is try to find out more about the rock, so he sends you to the Keldagrim Library for information.
The Keldagrim Library is located on the west side of the river, north of the Palace. Ask the Librarian about impenetrable rocks, and he will direct you to Wemund's Wrench Warehouse at the Keldagrim Palace. Speak with the Dwarven Engineer (not Wemund himself) and you will ask about Dondakan's rock. He will tell you that one of Dondakan's old colleagues called Rolad would know more, but that he left to go on adventures, and is currently a part of the Black Guard at Ice Mountain.
Rolad and the Missing Pages
Travel to Ice Mountain (between Falador and Barbarian Village) and speak with Rolad about Dondakan's rock. He tells you he came across a book that described this rock, but he lost the pages in the Dwarven mine below, and suggests you go find them.
Page 1: Kill scorpions (you may have to kill more than one)
Page 2: Search minecarts
Page 3: Mine any ore in the mine
Take all three missing pages to Rolad, who will exchange them for the Dwarven lore.
This book tells you that long ago, the Arzinian Being of Bordanzan was chased into this rock by using yellow power stones. Keep this book, as you will need it later in the quest!
For a quick return to Keldagrim, use the train cart located south of Nurmof's pickaxe shop. Return to Dondakan with the Dwarven lore, and you will tell him that according to the book, there is a demon spirit called the Arzinian Being of Bordanzan, as well as a large amount of gold, inside the rock. Ask Dondakan what he has tried to break the rock, and he will tell you that he tried steel, adamantite, and even runite cannonballs. Finally, he will kick the rock with his granite boots.
Use a gold bar on Dondakan and you will suggest creating a golden cannonball, which he will agree to. You can smelt the golden cannonball by using the gold bar on any furnace. Give it to Dondakan, who will fire it at the rock. The golden cannonball is absorbed into the rock, and Dondakan gets a brilliant idea: fire you out of the cannon, wearing a golden helmet. He gives you a part of the schematics to alter his cannon to fire a person.
A Really Smart Idea
Speak with the Dwarven Engineer at Wemund's Wrench Warehouse again to receive the second part of the schematics, and he will direct you to Khorvak, a dwarf at White Wolf Mountain, who gave him the schematics initially. Travel to White Wolf Mountain and use the shortcut (which you are allowed access to after the Fishing Contest quest) and go to the bar area. Pick up a Dwarven Stout on a nearby table and speak with Khorvak for another piece of the schematic.
Speak with Rolad and he will tell you he has a base schematic for a cannon, but he has misplaced it. Speak with him again and he will tell you he's not sure what he drew the schematic on.
Read the Dwarven lore and you will notice the base schematic is written on the back page of the book. Now that you have all the schematics, click one of them to attempt to assemble them.
To assemble the schematics you will need to use the arrows and the rotate button to line up the images so they make a complete schematic A good strategy is to hide all but one schematic, and to find the body part that lines up with the base schematic. The torso and legs are easy to find, but the head is a little trickier. The completed schematics will look like this:
The golden helmet is much easier to make, you simply need three gold bars and a hammer. Use a gold bar on the anvil and you will be asked if you want to make a golden helmet.
The Arzinian Mine
Get your combat gear, golden helmet, and pickaxe, and speak with Dondakan to be fired headfirst into a wall from a dwarven multicannon.
You will be fired into the wall, and find yourself in a large mine filled with gold. The Arzinian Being of Bordanzan threatens you with destruction, and your helmet begins to get heavier. You must make your way into the large center of the mine to fight the Arzinian Avatar, after mining as many gold ores as you can.
If you take your gold helmet off at any time you will be ejected from the mine, and if you stay in the mine for more than eight minutes, you will automatically take your helmet off, and you will lose all the gold ores you mined during that time. Note that you will not receive experience for the ores mined before you defeat the Arzinian Avatar.
You must mine at least one gold ore, or the Arzinian Avatar will not have a combat level, and be undefeatable. If you mine 10 gold ores, the Avatar's level will be 125.
After mining as much gold as you can, leaving yourself at least two or three minutes to fight the Arzinian Avatar, jump through one of the walls of flame to reach a large center of the mine. Talk to the circle of flame in the center, and the Avatar will attack you, using whichever style of combat you are weakest against; if your melee skills are the highest, it will use magic, if your ranged stat is highest, it will use melee, and if your magic stat is highest, it will use ranged.
When the Arzinian Avatar of Bordanzan is defeated, you will be ejected from the mine. Speak with Dondakan to claim your reward and complete the quest.