The first layer of Arborea contains Arvandor and Olympus, the two realms that the entire plane is known for. A basher'd think that the two realms are as close as two ale-houses in Sigil, the way they're always lumped together. Fact is, they're separated by hundreds of miles of unclaimed wilderness. The layer itself is slightly convex, so that while the realms of Olympus and Arvandor both occupy the highest pinnacles of land within their realms, neither citadel can see the other.
The layer is one of steep mountains cut by great passes and monstrous broadleaf trees rivaling the size of the redwoods of the Prime Material Plane. Its hillocks make the Clueless stare in slack-jawed wonder: The hills are mountains and the mountains are larger than anything but the earthbergs of Ysgard. Olympus's hills are covered with arbors of grapes, untended orchards, and fields of wild wheat. Away from the settled and claimed areas, the layer grows wild quickly. Fell beasts and creatures such as giants and cyclopes roam the lands to challenge berks seeking adventure here.