Between a Rock...

Walkthrough
You can use Prayer for an easy fight; the spirit shouldn't take too long to kill. If you are close to dying, you can take your gold helmet off, which will teleport you outside of the rock, next to Dondakan.
 * Start the quest by going to the Keldagrim mines (fairy ring code ), which can be found north-east of Rellekka. Upon entering the cave, right across from you will be a crack between two dwarf statues, which you should enter. From there, talk to the Dwarven Ferryman (make sure not to talk to the boatman) for a ride across the river, which will cost 2 coins or be free if you have a Ring of charos (a) equipped.
 * If you take the minecart from the Grand Exchange, go north-west from the carts to the Dwarven Boatman and take the boat (free) to reach the Ferryman at the entrance.
 * To your north is the quest start. Go to the east and go around the rock wall blocking you. Speak to Dondakan to begin the quest after asking, "Why are you firing a cannon at a wall?" and "So why were you trying to get through the rock again?" Finally, choose "Sounds interesting".
 * Dondakan will ask you to get further information about the rock, so return to the other side of the river, paying 2 coins again or crossing for free with the ring. This time, speak with the Dwarven Boatman to be taken to Keldagrim. If you have not started The Giant Dwarf, you will be presented with a small cutscene introducing the area and you will be taken by guards as well as having the option to start The Giant Dwarf.
 * Go into the western part of the Trading Consortium. Look for the area with an anvil on the minimap next to the general store and speak with the engineer.
 * You will be told to speak with Rolad located at the Dwarven Mine entrance camp next to Ice Mountain. To get there, either teleport to Falador and walk the distance or take the mine carts located in the southeastern portion of Keldagrim for 150 coins (75 coins if you have the ring of charos (a)). If you took the carts, head south, east, then north and exit the mine.
 * Rolad is inside the eastern house at the camp. He will ask you to find the pages from a book giving you information about the rock.
 * Note: Make sure to fully complete the dialogue otherwise the pages won't appear.
 * All three pages are found in the Dwarven Mine. Note that the pages may require multiple attempts to be obtained:
 * The first page can be found by killing scorpions in the southeastern area of the mines.
 * The second page is found when searching the mining carts.
 * The third page is found by mining most ore rocks inside the mine. (Adamantite rocks do not work, and neither does coal.)
 * Return to Rolad when you have found all three pages, and he will give you the Dwarven lore. When you have the choice, you can answer 'Of course', or lie to him and keep it. Read the book, and then keep it for later. If you need a cannonball mould, purchase it from Nulodion in the western house next door to Rolad.
 * Head back to Dondakan; if your house is in Rellekka, teleport there and head east to the Dwarven Ferryman, or go via the mine carts (paying another 150 coins or 75 with a ring of charos (a)) and Dwarven Boatman and Dwarven Ferryman. Speak with Dondakan. He wants a material that is stronger than runite and granite. This is where your gold bars come in handy.
 * Go to any furnace with a gold bar (you need the other three for later; do not make all four at once with the drop trick since your character can only carry one at a time) and your cannonball ammo mould, and make a golden cannonball. The closest furnace is the one in Rellekka, which you can use if you have completed The Fremennik Trials.There is one furnace at Zanaris also. Another option is to take the fairy ring to Edgeville or head back to the mine carts in South-east Keldagrim and take Cart 3 to the Grand Exchange; then, use the furnace in Edgeville by using the shortcut from the Grand Exchange to Edgeville (21 Agility required).
 * When you are finished, give the cannonball to Dondakan. When he fires it, the cannonball will disappear through the wall. He will then ask to fire you through the wall, but he needs the schematics to change the cannon to be able to fire a human. You will also need to make yourself a golden helmet if you don't want your head to explode when you hit the wall.
 * There are a set of four (4) schematics:
 * The first schematic is given to you by Dondakan.
 * The second one is given by the engineer back in Keldagrim. You can make your golden helmet while you're here; use your gold bars on an anvil. (Don't forget your hammer!) (If you do make it here, you may want to bank it before you get the other pages, as it is very heavy and will bring your run energy down very fast while running around for the other schematics.)
 * Read to the last page of the Dwarven lore book, and you will find another schematic page.
 * Teleport to Camelot, and enter the shortcut that goes under White Wolf Mountain, or go back to Keldagrim via the mine cart, and this time, take the mine cart to White Wolf Mountain (this ride costs 100 coins for one trip). Go to the small bar area, and speak with Khorvak. He will ask for a dwarven stout. You can take one off the table, and give it to him, or refuse and enjoy a funny piece of dialogue about RuneScape and alcoholics. Either way, you will receive the final schematic.
 * Once you have all schematics, click 'assemble' on the one Dondakan gave you. You will be shown all schematics, but they will not make any sense. What you must do here is move the schematics one by one so that they fit with the original schematic. Select and show one at a time, rotate and move them to fit. It may be easiest to use the human stick figure legs, torso, and head to position each of the pieces correctly. This part should be quite simple. Be aware that even if you the pieces in the correct relative position, you might need to select them all and move them together to the correct position on the screen. Once you put them all in place, the screen will show: "That's it! It all makes sense now! If you were a dwarf, that is...".
 * Travel back to Keldagrim, bank, get combat gear, pickaxe, and if needed, go back to the engineer in the Trading Consortium so that you can make your helmet by using your remaining (3) gold bars on the anvil if you haven't made it already.
 * Equip the golden helmet; make sure you have a pick because any gold in inventory will disappear. Go back to Dondakan with the schematics and the items needed to kill the level 75-125 enemy. Once you are ready, ask Dondakan to shoot you into the rock.
 * To fight the Arzinian Avatar, you will need to mine at least six (6) gold ore. Mining 15 is highly recommended as this will lower the combat level of the boss from 125 to 75. Make sure you keep this gold in your inventory. You only have eight (8) minutes to mine the gold and defeat the avatar; if you take off your gold helmet, you will be teleported back to Dondakan.
 * When you feel you have enough gold, go to the centre of the area, where you will find a set of flames. Go through the first set of flames and talk to the second set. While talking to the flames, the Arzinian Avatar representing the demon will come and attack you. The spirit will attack with Magic, Melee or Ranged, whichever is the natural weakness to your strongest on the combat triangle.
 * When you have defeated the spirit, you will be teleported back out of the rock. Speak to Dondakan to finish the quest.

Rewards

 * Quest points
 * Defence experience
 * Mining experience
 * Smithing experience
 * A rune pickaxe
 * The ability to teleport to Dondakan's rock using a ring of wealth
 * You get to keep your gold helmet and can continue using it to fire yourself into the rock to access the Arzinian Mine where there are lots of gold rocks and gold veins, and a nearby dwarf banks the player's gold ore for a charge (he keeps 20% of the ores, rounded up, or 10% of the ores if the player has the ring of charos (a)).

Trivia

 * After the quest, you may attempt to make an offer to buy Dondakan's Granite boots, but no matter how much you offer, he will never sell them.