The Inner Planes were a subset of the known planes of existence. They were the source of the fundamental building blocks of matter and energy for the entire multiverse. The Inner Planes contained environments that were among the most hostile in the multiverse. Unlike the Outer Planes, which were built on belief and thought, the Inner Planes were the manifestation of central aspects of physical reality. As a result of this intense concentration of reality, everything in the Inner Planes, including its inhabitants, felt more vivid and intense, while at the same time more indifferent.