This is going to be a brief guide! You can be level 1 and do this (theoretically). I think my lowest was around 10.

There's tons of Throwblasts in the Warrior's Respite where you find Barroch. You don't need every single one of them, but it helps just in case you miss. Grab them all.

When it comes to the eyeball fight itself, patience is key. Stay away from the tentacles, and just kinda dodge him for a while. The only part of the fight that matters is when the orange puddles appear on the floor and a large tentacle comes out of the ground. These tentacles topple the Gazer.

Just park your little body right under the eyeball and let the tentacle do all the work. Once the gazer falls, start pelting its protruding eye with the throwblasts.

For added fun, you can also buy a Pilgrim's Charm from Barroch. Use it within the last minute or so before killing him for an additional 225k (I think) EXP.

... For further added fun, if you're a ranger or assassin, you can sprint through the next area and knock that big ol' reaper off of the bridge before the charm expires. Doing these two things will get a level 15 character to level 95 or so almost immediately.

Have a shamelessly self-promoted video.