On the Map 8 - Follow the tunnel all the way to (C-7), where you exit back to the jungle.
There are two Flame Spouts on the way.
These will go down on their own within approximately 5 minutes (3 hours game time).
Be alert of the Ash Dragon near the end (before the last Flame Spout). It has a wide sight and sound detection range and uses Draw In. Time it right and you can walk into the tunnel without a problem when it is far enough from the entrance.
Now that you're in Yuhtunga Jungle again, go to (K-7) by following the left wall. You will come to 2 waterfalls, each with a tunnel behind it. Go through the one closest to you (northernmost) of these tunnels to reach Cermet Headstone, located a few steps into the cave at the NW edge of (L-7).
If you are traveling from the Cloister of Flames home point: Head to the J exit on map 7 at G-3. Then take F exit on map 3 at E/F-11. Then take A exit on map 2 at K-7. Then take exit B on map 1 at F-8. Then take exit D on map 2 at G-11. From here travel the original route above.
Gravity and Bind work, but it is worth noting that they easily lose interest if ventured too far from and if not aggravated soon enough, will regenerate HP quickly like any unclaimed monster not engaged on a player character.
After defeating the Opo-Opos examine the Cermet Headstone again to receive the key item.
Follow the uncharted path leading towards north, to (I-7) to find the headstone.
The Doomed named Doomed Pilgrims spawns here when the stone is examined. It is generally regarded as the most difficult of the headstone fights. It hits hard and fast, so be careful. High evasion works well.
Somewhere on the island of Zepwell lie the remains of an ancient temple.