u]Walkthrough[/u]
Enter the area and go past the Ghostly Heroes to the glowing circle. Step into it to get the Divine Fire enchantment. Step onto each of the three rune marked rocks, they'll glow even brighter when they're stepped on, and the three seals on the front of the mesa will light up. Once all three are lit, a cutscene will play, and you will be teleported inside the mesa. Defeat the doppelganger there.

BONUS Defeat the Doppelganger in under 10 minutes.