Feywild
From Syra D&D Wiki
The Feywild is a demiplane that overlaps with and is parallel to the material plane.
It was one of the original demiplanes, along with the ethereal plane and the plane of shadow, and the plane of origin of many fey species, including gnomes. Three thousand years ago, when Lolth and the drow were warring against Corellon, a large number of elves hid themselves in the Feywild in order to escape the chaos. For reasons that have long since been forgotten, the Feywild became disjoined from the material plane and all connection between the two was severed, trapping all of its inhabitants.
Recently, due to the chaos of the Deity War, the Feywild began to reconverge with the material plane. The first signs of this were subtle, and consisted mostly of an increase in fey activity. One of the other signs was that the gnomes began to experience an odd sensation in the back of their minds. Though they did not know it at the time, this was due to the renewed proximity of the Feywild causing their fey ancestry to begin to assert itself. Eventually, this feeling led Gurrard and two of his former adventuring partners, Myra Brigg and Priam Adenis, to investigate. Their investigation led directly to the rediscovery of the Feywild and the beginnings of diplomatic relations with many of its inhabitants.
One of the most notable things that came from the reconnection of the Feywild was the rediscovery of the elves who had been trapped there. Their time in the Feywild had caused their descendants to evolve beyond their elven heritage into the eladrin.