Pyrulea is an odd plane that Dyfed escorted Yawgmoth to in order to prove her abilities as a planeswalker to him. It is composed of a densely forested sphere around a central star; the plane's inhabitants live on the interior surface of the sphere. What's more, the size of the plantlife is particularly enlarged.
From J.Robert King's Novel: "In every direction, a vast rain forest spread. Millennial trees trailed nets of vine and moss hundreds of feet downward to wet undergrowth. [...] North, south, east, and west, the landscape curved up and away into walls. They, in turn, joined to form a ceiling of sky. This was not merely a bowl of land but the inside of an enormous sphere." This plane is an example of a naturally occuring Dyson Shell.