The Forest, or the Old Terrritories, was where the Clans lived before the Twolegs took over. All books taking place during or before Dawn were set in the Forest.
Despite its name, only a small part is actually forest, mainly ThunderClan territory. WindClan's territory was a hilly moorland, ShadowClan's marshy land with some trees, and RiverClan's an inlet in the river.
The site that the Forest is based on is the New Forest in England. However, some of the areas are more fictional. (i.e. Highstones and the mountains nearby)
The LakeThe lake is not based anywhere, it is completely fictional. ShadowClan's territory is a pine forest, WindClan's hilly moorland, RiverClan's wetland and ThunderClan's a forest.
The GorgeThe gorge is a sandy gorge where SkyClan dwells. It is a fictional place and no relation to the gorge in the old forest.
The MountainsThe Mountains is the home where the Tribe of Rushing Water dwells. It is a fictional place set in between the forest and the lake.
The tribe's mountains can be found in the center of this map.