If you were not able to find it, go down and throw a Teleport Pyramid into the chamber from the south, then step on the pressure pad inside to open the gate. Use a characters with high Perception to find a hidden switch on a wall to the right of the stairs and to the left of the door. Return to the central chamber and go upstairs. Step through the mirror, collect the Earth Key, and retrieve your Teleport Pyramid. Throw a Teleport Pyramid into the treasury and travel inside. You must solve the puzzle and destroy the correct statue based on the clue that is given. You must destroy one of the statues, but if the incorrect one is selected you will teleport to the start of the temple. Save the game, as another puzzle must be solved. Activate the "Source Temple Vault" waypoint to enter the Source Temple Vault. Teleport across the hole and search for a door to open past some wreckage to reach a teleportation waypoint. Throw a Teleport Pyramid across and teleport to the other side. Go through to enter an area with a broken bridge. Search the walls to find a hidden button that opens another doorway. Once inside, bypass the poison gas trapped pressure pad. Stand on the pressure pad found there to open the left door that opens into a third room.
Stand on the pressure pad close to the giant head, then enter to the room to the right. There are pressure pads in each room, but some are dangerous. Stand on the floor panel switch to open the first door. Once you enter the Source Temple, there will be a huge puzzle in the central chamber with three Statues of Self-Awareness. All enemies from random encounters in the overworld map can be killed using this method. Take the barrel out of your inventory, then use Telekinesis+2 to slam it into your enemies and instantly kill them. During combat, open your inventory menu and send the Beer Barrel to your main character. Get into a random encounter outside Cyseal. Switch back to your main character and leave the secondary character with the barrel. The barrel will overburden that character, making them unable to move. Once there, switch to your secondary character and place the barrel in their inventory.
Look for a large beer barrel on stilts behind some wooden barriers and up some steps. Go on the road northwest of the market square. After getting the Telekinesis+2 ability, go to Cyseal.