After dozens of failed expeditions, we've finally found it. This has to be the lost city the Wood Elves call Root Sunder. Our maps of the era suggest this would have been an ideal location for a trading hub. The only hurdle would be taming the jungle. Not a small hurdle, but one the builders of Root Sunder believed could be overcome.
And their solution, whatever it was, clearly didn't work. But they've infused this place with a strange current of magicka, funneling through the central Welkynd Stone and to a chamber below. If we could unlock the door, perhaps we could learn more.