You can start the quest by interacting with the Sage Stone in The Shivering Plains. The Sage Stone is on the northwestern coast of the region on a cliff.
||I found a Sage Stone in The Shivering Plains. The Stone has tasked me to prove myself before it'll open...
The task is to gain at least 50% happiness in any region. Happiness is gained by clearing the Murk, farming, finding sprites, completing quests, and planting trees.
Talk to the Sage Stone again when one of the regions reaches 50% happiness to complete the quest and access the teleport.
Completing this and every other Sage Stone quest unlocks Rock of Sages steam achievement.