AboveAll the space that occupies life and air above the passages. Sometimes referred to as the Upper Regions. This is the area that humans typically are aware of. It is here that light is provided by the sun, and other more normal means.
BelowAll the space that occupies life and air below the passages. Travel to this region is specifically restricted to trapdoors that open into the passages, in turn allowing those lucky enough, or unlucky enough entry into the Below. Light here is created by artifical means, and sometimes requires using energy from Above.
The PassagesSimply put, these are the tunnels that convey trapdoor passengers to the Above and Below. Each passage has its own personality - meaning, they can be unpredictable. Sure, most of the time you will arrive at the appropriate destination, but there is always chance of not arriving at your first choice. Or, it's possible you might not arrive at all.