Overview
"Unravel the secret of the Ancient Ruins" is an objective during the Reunion main quest in Chapter 2 of Crimson Desert. It requires you to learn a new ability, enter a hidden cave, and solve a three-platform puzzle inside. There is also a bonus collectible nearby that is easy to miss.
Step 1: Learn Nature's Grasp and Enter the Cave
When you reach the Ancient Ruins, look for a blue silhouette of a child. Use your observation ability (L1 / LB) to watch the silhouette and learn the Nature's Grasp skill. This is Kliff's ability to manipulate the environment using Axiom Force.
After learning the skill, target the blue-highlighted wall at the ruins entrance. Activate Nature's Grasp (Triangle + Square, then X on PlayStation; Y + X, then A on Xbox) to raise the wall and reveal the cave entrance. Walk inside.
Step 2: Solve the Platform Puzzle
Inside the cave, three round platforms are embedded in the wall. You need to strike them in the correct order using Force Palm (hold R3 / Right Stick).
Hit the platforms in this sequence:
Middle platform (the center one)
Left platform
Right platform
When struck in the correct order, all three platforms slot into the wall simultaneously and energy begins flowing through them. The puzzle is complete.
Step 3: Speak with the Child
Exit the cave after solving the puzzle and speak with the child waiting outside to continue the Reunion quest.
Bonus: Abyss Cresset Collectible
Before leaving the area, check for a small pillar near the cave entrance. It holds an Abyss Cresset. Collecting this item awards an Artifact / Skill Point and completes the challenge "Abyss Cresset of Meandering Hills." These collectibles are easy to walk past, so take a moment to grab it.
Tips
If the platforms do not respond to your strikes, make sure you are using Force Palm (hold R3 / Right Stick), not a regular melee attack.
The correct order is always Middle, Left, Right. There is no randomization.
The Abyss Cresset collectible is missable if you leave the area without picking it up. Return later if needed, but it is easiest to grab now.