When Barbarella meets Mark Hand, he tells her they're in the Iceland Forests of Weir on Planet Lythion.
The forest appears as nothing but ice and snow. Giant crystals and frozen lakes cover the area, along with other crashed ships. Whether or not the whole planet was covered by the forests was not made clear.
According to Mark Hand, all children lived in the Iceland Forests until they reached a servicable age for the Great Tyrant.