Oindora, the great ruined Eladrin city, is one of many such cities in the Feywild
The Feywild is perhaps the closest plane to the prime material plane, existing alongside it throughout its entirety. It is a plane of natural wonders - the greenest forests and the deepest canyons intermingle with the deepest of lakes and the most dramatic of waterfalls. The ever-blue sky can be seen by denizens throughout the plane, except for those who unfortunately are caught in a storm, rising with surprising speed and intensity.
The Eladrin consider the Feywild Home, despite the fact that many of their cities lay decimated and abandoned after the great Eladrin-Drow war. Those who would seek it out would do well to find a fey crossing--the portals between the prime material plane and the Feywild--or a worldfall--essentially an entire Eladrin city that travels between the Feywild and the prime material plane.