Metahedron

The metahedron (also known as the tetrahedron) was created by the grey man at the same time as the city of Cathedral. It was an extension into normal space of the city, and could be used to make a gate for transportation to it. The metahedron's primary purpose was to change the structure of reality. To prevent it from being destroyed, it moved to a different planet every eighty thousand years. When Cathedral ceased to exist, the metahedron crumbled to dust. (PROSE: Falls the Shadow)