Seeds of Feywild plants that once fully grown will create a Feywild portal - a veil between the prime material plane and the actual Feywild world were the fey live.

The Feywild Forest is named that because it is magical by it own nature and has many fey that choose to live in it. Most of the fey are friendly, but not all of them. There are also portals that are vails into the actual Feywild within this forest.
... Feywild Forest

The Feywild and Shadowfell surround our material world and are are kind of reflections of our material world - The Feywild being bright and cheery while Shadowfell is dark and gloomy.
... Feywild