(NOTE: Since the Death Plateau quest has been updated; you won't be able to get into the arena until you finish the newer version first.)

(NOTE: You may start the quest even if you are in the midst of delivering supplies to the Ambush Commander.)
Safest Route To Troll Stronghold

The safest route from Burthorpe to the Troll Stronghold. (The teleport route cannot be used, because it requires Eadgar's Ruse which in turn requires this quest)

To start, speak to Denulth in Burthorpe; who is east of the bank. Ask him about the ongoing battle between the Imperial Guard and the trolls. He will tell you that their plan of ambushing the trolls backfired; they were attacked and Dunstan's son, Godric, was kidnapped and taken to their stronghold.

Tell him that you would like to help get Godric back. Head to Freda and buy off a pair of climbing boots for 12 gold coins. With the boots, enter Sabbot's cave (north-west of the defensive wall) and work your way through the obstacles leading to the site of Death Plateau's final ambush.

Directly to the northwest of the cave entrance (ambush area) is an agility shortcut as shown on the map. Put your boots on and climb over this wall of rocks. This is the part where you need 15 agility. Then go east, climbing over the various rock piles that you encounter, and enter the arena.
Fighting DadEdit
Dad

This is where players meet a huge troll called Dad. He will say that nobody goes past without defeating him. He is level 77 and uses a giant log as a weapon. He can hit over 250 and send players flying, stunning them temporarily.

There is a safespot for Dad; enter the western end of the gate, and then let him speak, and stand right beside the gate on the northern end, where you can safely range or mage him.

Also DO NOT exit back through the gate as you will find that Dad will have his life points fully replenished. Prayer can be used here, but it may be best if you save it for the Troll General (level 91, 171) later on, unless you have a prayer potion or plan on making a return trip.
Dadsafespot

Safe spot for Dad

When Dad is on low life points, he will ask you to spare his life. You can either choose to spare his life or you can kill him. It is recommended that you spare his life. If you decide to kill him, the Troll Spectators(level 65) will try to attack you, and Dad will just respawn later on. At this point you are eligible to enter the God Wars Dungeon.

You can now pass through the northeast gate. Go past the level 74 and 75 mountain trolls, and enter the cave at the end of the path. Continue through the cave, and exit it at the end. You should now be at a spiral mountain. Do not climb the mountain, but make your way around the mountain, which is located to the south-west of the cave exit, to reach an area full of mountain trolls, similar to Death Plateau.

After entering the troll camp, run north, and you will see a winding path that leads to an entrance to the Troll Stronghold. Go up the ramp and into the cave, using protect from melee to avoid combat with the trolls inside.