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 which can be found northeast 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 dwarf ferryman for a ride across the river, which will cost 2 coins, or be free if you have a Ring of Charos (a) equipped.
 * To your north is the quest start, but to get there, go to the east and go around the rock wall blocking you. Speak to Dondakan to commence the quest.
 * 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 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.
 * To the south of where the boat landed is the Trading Consortium. Enter this area and go up the stairs. Go to the west side of this floor and go down those stairs. Look for the area with an anvil on the mini-map and speak with the Engineer.
 * You will be told to speak with Rolad. Go back to the east side of the Consortium. Exit the Consortium and go in a southern direction until you find the mine carts. Pay up 150 coins for a ride to Ice Mountain. Go to the ground floor where the dwarves are located, not the Falador exit.
 * There will be two houses in front of you. Go in the eastern-most one and speak with Rolad. He will ask you to find the pages from a book giving you information about the rock. If you don't have a cannonball ammo mould, go to the other house and buy one for 5 coins from Nulodion.
 * All 3 pages are found in the dwarven mine:
 * 1) One of them can be found when searching the mining carts
 * 2) Another is found when killing scorpions (may need to kill more than one)
 * 3) The final one is found by mining any ore (may need to mine more than one)
 * Return to Rolad when you have found all 3 pages, and he will give you the Dwarven Lore. When you have the choice, answer 'Of course', do not lie to him. Read the book, and then keep it for later.
 * Head back to Dondakan via the mine carts (paying another 150 coins) and speak with him. He wants a material that is stronger than rune and granite. This is where your gold bars come in handy.
 * Go to any furnace with 1 gold bar (you need the other 3 for later) 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. Bring the cannonball back to Dondakan. When he fires it, the cannonball will disappear through the wall. He will then ask to fire you through the wall, but 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 4 schematics:
 * 1) The first one Dondakan gives to you
 * 2) 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).
 * 3) Take another cart ride back to Ice Mountain and speak with Rolad for the third schematic. He will say the he lost it. Search the last page of the Dwarven Lore and you will find the third schematic.
 * 4) 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. Take one off the table and give it to him, and in return, 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. This part should be quite simple. 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...”.
 * Equip the golden helmet and 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.
 * Now that you are inside the rock, you are surrounded by gold ore and gold veins. Mine as much as you can; the more you mine, the weaker the enemy will be (Note: you only have 8 minutes in here, so be swift). You must mine gold to kill the spirit; without gold, you are fighting for a lost cause.
 * 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 the Arzinian Avatar representing the demon will come and attack you. The spirit will attack with mage, melee or ranged, depending upon which is your weakest.
 * When you have defeated the Spirit, you will be teleported back out of the rock. Speak to Dondakan to finish the quest.

Rewards

 * 2 quest points
 * 5000 Defence experience
 * 5000 Mining experience
 * 5000 Smithing experience
 * Rune pickaxe
 * You get to keep your Gold Helmet and can continue using it to fire yourself into the rock. Inside are quite a few gold rocks, and a nearby dwarf banks the player's gold ore for five of them. Players who have the Ring of Charos (a) can reduce the price to three.

Trivia
After the quests, 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.