I ran it last night. I'm posting this because it was my first run and it was painful. Nearly an hour and a half of pain at level 35. We died at the end. Ran out of time. So you can avoid your first run through the sunken temple being a major disaster, I have decided to share my experiences.
This quest is optional. Not required for the story. The unlock is easy to find if you are progressing through the story around level 33 or 34. (I have a crazy tendency to go to everyone with exclamation points over their heads and ask them "Hey, what's wrong?" Some telltale signs to watch for so you can unlock dungeons like the sunken temple are the exclamation points that pop up new in areas where you have already cleared all the quests, but are told to return there to complete part of the story mission.
Anyway, I did this quest as a 35 black mage. It gives great exp, I leveled half my bar to 36 in the 90 minutes I was in. But I am going to wait a few more levels before I try again, and will likely run it with ZAM folks. Random duty finder is too much of an incompetence lottery (with myself included as one of the incompetent).
1. I moved in to the mission with three random folks. We had a tank, a close range DD, me (as black mage), and our first healer was a Scholar. I don't know if this has anything to do with the player or the job, but the WHM we got later did a much better job. More on that later.
2. Our first wipe was at the 1st mini boss. I remember this guy from FFXI when I was out grabbing blue mage spells. This guy is stronger than those weaklings. He is basically a giant minotaur who casts Doom on you. At 50% health he starts to do this. To remove doom, stand on the panels on the floor. That is what our ACN told us. We wiped. The key missing component, There are three panels that randomly glow, you have to stand on the one that is currently glowing to remove doom. He also does a major punch that can stun you. Finally, throughout the battle he adds bees (two at a time) that seem to directly target the healer. If you are DD, kill these ASAP. Other than that the battle was ok.
3. After the first wipe at this guy, the ACN quit out of apparant frustration that we couldn't stand on the right tiles. I mean, if you are instructing me and you want me to stand on a spot (and there are 10 spots) don't tell me, "Go over there to the spot that is next to the other spots." Wasted 15 minutes there. Got a new healer, a WHM from Ultros (not in ZAM, don't remember the name) who was much better. Entered with the phrase "I hope you guys are better than my last party". Apparantly there is a lot of healer frustration from this dungeon.
4. But I digress. The next boss was a big stone guy with a crystal in the middle of his chest that just won't go away. You have to kill the crystal before you can damage the golem, and then when you get a change to do that, zerg the heck out of him because he only holds like that for about 30 seconds before the crystal reforms on his chest and you have to kill it again. This guy hits hard, but he is manageable. We had to cycle the crystal 4-5 times to beat him. No adds (thank Eorzea) but he has some circular and straight line aoe that seemingly aims for the squishy people (even in the absence of hate) so be careful. But this guy easily took us 15 minutes to beat going full force. Titan.... bah. Try this guy at level 35!
5. Dont forget that there are treasure rooms right off of the boss room before you go in. We didn't put something in the right place apparantly because the items I got lotted were named things like "greasy" this and "old" that.
6. Finally the boss. A giant miserable tiki totem looking fool that relies on his buddies the staves to deal all his damage. Early on the battle is easy, you are beating away, a big floating stone head spawns as an add, you kill it, go back to beating, then another kead, kill it, rinse and repeat. Then a big staff appears in the ground and starts shooping blue lasers that will fry anything squishy in 1-2 hits. And it shoots them literally every second... at the DD... because it likes to go after its attacker. And each one takes three DD spells to kill (at lvl 35 with best gear). And it spawns them until the screen is full of blue lasers like Mission Impossible if you let it. The key is to kill these things immediately when they spawn. Actually they are manageable if the party goes after them and is aware. Then at a little less than 50% health, the boss makes it impossible. He spawns the staves at the four corners (one sometimes two at a time) inside a blackened area. I learned the hard way that I can't long range nuke these things after 3-5 seconds because a barrier goes up that prevents physical entry, attack entry, magic entry, everything. The whole blackened area goes up in a protective shroud for 5-10 seconds and shoots 3-5 beams of mage toasting blue light. So the key is to get inside the blackened area before the barriers go up so you can kill it. The problem is that unless you split your party to the four corners you will have a tough time tackling these plus the boss We got him down to 10% heath before our wipe. Blue light killed the squishy peoples. Took about 15 minutes to get him down to 10%. After that, sadly, we were left with a measly seven minutes to shortcut back and start over. We all got in with 6 mintes left and proceeded to demonstrate what it would be like to ignore adds. So after a screen full of blue lazer beams... we have our third party wipe. I got some greasy items, half an xp bar, and some painful, but useful memories.
This guide was created to literally save you 90 minutes (assuming you have never ran the temple).