Vallestrella is a parallel world that is magical in nature, and home to the mystical creatures known as Jaquins, and is ruled by King Verago, Skylar and Nico's father. The entrance resides in a hidden cave that only Jaquins can access.
Humans are not allowed there, because years ago, a human accidentally released Kirin, an evil monster the Jaquins had their biggest battle against, and won, but at a cost, and there are other dark forces imprisoned in Vallestrella as well, such as Marimonda, an evil forest sprite who tried to destroy every city in Avalor centuries ago, but was stopped by the sun birds with ancient magic. The entrance is first shown in Flight of the Jaquins, when Skylar picks up Ciela, Avión, and Nico for Guardian training. The inside of Vallestrella is first seen when Skylar, Luna, Migs, Nico, Elena, and Mateo go there to request that Nico get a second chance to take the test he just failed.