This is a not-so-hidden quest because you can either start it by talking to Sosi or finding at least 1 inscription that can only be found using Sorush, the new gadget that can only be obtained after starting Khvarena of Good and Evil. So make sure to complete that one first! There will be a hidden achievement after completing this quest~
Khvarena Inscription Fragment
➥ The quest won’t show you the locations of the inscriptions so you can rely on my map above for all 4 inscriptions’ locations. Remember that you can see the inscription only after using Sorush.
1. Teleport to Vourukasha Oasis’s south waypoint and walk forward a little bit to the protruding rock beside the leaf parasol. Then, equip your Sorush to see the inscription on top of the rock and pick it up to start the quest. You can either continue searching for the remaining inscription using the map I include above or talk to Sosi first (I choose the former so let’s continue searching for the inscriptions).
2. Teleport to Hills of Barsom south waypoint (near the domain) and head to the huge tree. The inscription is at the opening of the said huge tree.
3. Teleport to Tunigi Hollow southwest waypoint and head north to the biggest spike/tree. The inscription is at the top of said branch, so you need to use several Four-Leaf Sigils to glide to the middle part of the tree and use Sorush to reach the top.
4. Teleport to the Asipattravana Swamp south waypoint and head west to the large entrance that leads further to an underground cave. The inscription is on top of the huge entrance.
Talk to Sosi
➥ Now that you’ve triggered the quest (whether you’ve collected the remaining inscriptions or not), follow the quest navigation and talk to Sosi. She will request you investigate a few Fatui camps.
➥ Teleport to the Gate of Zulqarnain south waypoint and follow the navigation to the first Fatui Camp. Defeat the Fatui army there and investigate the note on top of a box.
➥ Investigate the next Fatui Camp south of Tunigi Hollow, defeat the enemies there, and investigate a bag in front of the bigger tent.
➥ Change your in-game time to between 10:00 – 14:00 and go to the main camp south of Samudra Coast by following the quest navigation. Keep following the footprints and you will fight some Fatui soldiers.
Place the Monument
➥ Teleport back to the Gate of Zulqarnain waypoint to the cliff and return all the inscriptions to the rocks behind Sosi. Defeat some Fatui again to complete the quest and obtain the hidden achievement “This Mystery Is Solved!”