Sildëyuir
More than two thousand years ago, the depths of the Yuirwood held the realm of Yuireshanyaar, home to the reclusive star, or mithral, elves. Faced with aggressive human settlers along the Wizards' Reach (most from Old Unther) carving out lands of their own from the ancient forest, the star elves decided to withdraw from Faerûn. Their High Mages forged a forest-wide network of stone circles and then worked a mighty spell through the standing stones that created a demiplane for the star elves to call their own. Most departed Faerûn at that time.
Sildëyuir is a plane of eldritch beauty, a land of perpetual twilight illuminated by a host of glittering stars. It extends about as far as the forest's borders, and like the Yuirwood, is an unbroken expanse of deep green dells and hidden brooks. The star elves raised great glass citadels for themselves and live there still, masters of song magic and lords of this fey realm.