Circle around the obelisk to find the stairs leading down just south of it. Alternatively, there are entrances accessible by flying mount on the side of the mountain on the southern and northwestern sides. At the base of the stairs on the high platform is the Titan Mechanism, where the quest will be completed. Look to the east. Down a level on the floor of the cave is the Titanic Guardian. Use the activation device to activate him. It is a level 85 elite with 232k+ health. This is effectively a boss fight, but quite soloable.
It has the following abilities:
[Blazing Eruption]ωϖ—Erupts with flame in all directions, creating fire pools randomly within a 0 yard radius. These pools deal Fire damage on impact. A flame circle appears on the ground where the fireball will land, which hits for ~5500 Fire
[Burning Gaze]ωϖ—Channeling fiery rays of destruction. Hits for 4400-4800 Fire
[Summon Meteor]ωϖ—Summoning an Orb of the Sun Launched at a random unit fighting him. Units where it will land are inflicted with..
[Burning Adrenaline Rush]ωϖ—Movement speed increased by 50% Lasts for 5 seconds. If players don't get out of the way...
[Meteor Impact]ωϖ—Deals Fire damage to nearby enemies, knocking them back Hits for ~6k Fire
[Backlash]ωϖ—Deals Fire damage to nearby enemies, knocking them back. Hits for about 75k on the Titanic Guardian when its Meteor is thrown back at it.
[Decrepit Ruin]ωϖ—Movement speed reduced by 50% A persistent debuff on the guardian only.
Try to keep the Guardian at range, as it will melee. Melee players need not worry, as the guardian will throw meteors on occasion, which can be thrown back at the guardian to deal huge amounts of damage.
Watch out for the Blazing Eruptions, which are marked on the ground a few seconds before they land, and dodge his eye beam. He will throw the meteor, which "debuffs" players with the Burning Adrenaline Rush, which should be used to escape the immediate area or take ~6000 Fire damage.
The meteor, when it lands, triggers a boss warning:
Use the meteor to launch a critical attack on the Titanic Guardian!
Right-click on it to launch it back at the guardian.
It is quite possible to end the fight without taking any damage at all. Once the Guardian is down, loot the lens and head back to the elevated platform.
On complete, a big explosion happens and some fire and light shoots up. Head back to Harrison on the surface to continue.
Note:Though you can activate the Guardian from the platform, it will evade and possibly despawn. This fight must be done from ground level.