The Chains that Bind Us

Checklist

• Get Mission.
• Talk to Iron Eater.
• Go to Quicksand Caves G-11 ???
• Battle NM anticans.
• Go to Quicksand Caves H-8.

Strategy
I recommend a party of 6x 70s or 12x 65s for this, though that's somewhat approximate. Bringing poison potions and silent oils is a very good idea.
The hard part for this mission is finding everything. In West Altepa, head to the G-6 entrance of Quicksand Caves. Once inside, sneak your way down the main hall south to J-8 and then west to a door at H-8 (one of the weight activated doors). From there move south through more doors to G-11 where you find the statue everyone's talking about, and a ???
Have everyone drink a poison potion before touching the ??? because the anticans will cast sleepga on you. Fight them in the order "TPC" (first letters of their names).
Then touch the ??? again for a cutscene. Once you've all seen it, escape back outside.
The battle part is over, so you can dismiss any extra muscle you brought at this point. Then I recommend getting chocobos in Rabao because the next entrance to quicksand caves is a bit far.
Head to West Altepa's C-11 / D-11 border and move south off the edge of the map. The entrance you want is in D-12.
Inside, take the door at K-8 and hang a left, going north, east and south around corners to another door at G-8. The mural room at H-8 is just inside, and you'll find another ???. This one brings only a cutscene, after which you need only report back to Iron Eater.