Greenwold

The Greenwold is a copy of the material plane kept in stasis at a particular point in time. After the First War of Yarradon, a great Elvish empire covered most of the material plane, and with it grew a sprawling forest. When the empire began to sour and a revolt seemed likely, the one thousand most powerful magic users came together to try and save the forest by making it indestructible. Through a slight misunderstanding of magic on this magnitude, they did not save the forest on the material plane, instead they created an exact copy of the geography of the Material plane at that point in time (though with no sentient life other than themselves). The magicians believed they had succeeded though the cost of the spell was all sentient life, in fact they were on a separate plane of existence.