Sometimes during your exploration in the underground part of Chasm, you will find glowing secret messages/abyssal runes on the wall. But when you try to interract with it and get closer it will dissapear, just to appear again later after you take some distance.
That thing/secret messages/abyssal runes is actually part of achievement: The Nine-Word Rumor. It will dissapear if you have Lumenstone Adjuvant equipped, so you will have to unequip it if you want to observe all secret messages.
Here’s locations of all secret messages, scattered across The Chasm underground:
Location 1
Head to Chasm Main Mining Area teleport waypoint, glide down and walk north passing the bridge. After you arrive in this location, Cryo Abyss Mage and Electro Abyss Mage will spawn.
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Location 2
Can be found at the ruin across teleport waypoint.
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Location 3
Can be found near Ruin Grader.
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Location 4
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Location 5
Can be found at the ruin behind Ruin Grader.
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Location 6
On top of the same tower as secret messages 5.
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Location 7
Can be found in the room below serpent knight Hyglacg.
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Location 8
West of Glowing Narrows teleport waypoint. If you can’t seem to observe this runes, try to climb the wall until observe option appear.
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Location 9
Head to nearby teleport waypoint, then glide down.
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