The Tetracosmos is the complete universe where the story of Pantagrame Quest unfolds.
It is a hyperdimensional tetrahedron (a pyramid made of four equilateral triangles). It does not have any general geography and cannot be embraced by the human gaze or reached by human actions.
The Tetracosmos embodies the Solworld, the flat world populated by humans, as one of its facets. It is likely that all four facets each represent a world.