Mystery of the Crystal Skulls is a challenge in Tycho's Ribs to destroy all ten of the mysterious Eridian Crystal Skulls.
- The 1st Skull is in the same room as the fast travel in a corner.
- The 2nd Skull can be seen in a slot in the middle of the spinning object in the center of the chamber. It can be seen from the ledge after walking out the first rooms.
- The 3rd Skull is down the path hidden in a spire of purple crystals.
- The 4th Skull is a level down in the side room, the Compression Chamber. It is on the elevated alcove next to the jump pad.
- The 5th Skull is inside the room farther down the path, the Particle Collection Chamber. It is on one of the pillars connected to the spinning object in the center of the room.
- The 6th Skull is another level down, in the room with the claptrap unit, Z8N-TP. It is in the first alcove to the right.
- The 7th Skull is obtained by getting on the last elevator and getting off the second floor. Part of it is hidden in snow.
- The 8th Skull is on a ledge below the impassible ice path.
- The 9th Skull is in a square room with 4 smaller spinning objects behind the far corner from either entrance.
- The 10th Skull is on the structure just before the exit to Elesser.