Vien Forest is a forest located in Almia, near Vientown. It is a huge part of forest that have been inhibited by many Pokémon.
The Vien Forest has experienced a fire once, when a boy from Chicole Village named Ollie accidentally poured the Gigaremo's oil and burned the forest. Then, the local Vientown Rangers acted to the rescue. Sadly, some part of the forest that is badly burned cannot be restored to its original scenario, until the main character beats the game and do a Quest where Celebi, with his/her power restored the forest. The forest also has a hidden part of line which can only be travelled by using the Area Move River Flow after completing the Mission: Get the Blue Gem. Deep within the secret part of the forest, a rock statue is located. By using the field move 5 crush that is owned only by Garchomp the rock statue will transform into Regirock. Regirock is later required with Regice and Registeel in order to capture Regigigas that lies deep inside Hippowdon Temple after completing the game.