The abyss is a steep wall, reaching left and right for as long as
anyone has ever travelled, up at least ten thousand levels from where I
sit, and (in myth) down to the depths of Sheol, where the air burns, and
the face of the abyss wall melts and runs perpetually downward, into a
molten infinity.  Standing on one of the switchbacked roads that men
have scratched into the wall, looking out away from the wall, there is
just darkness, fallers, and debris.  Down and out, an occasional red
glow from (one supposes) Sheol appears, but nothing else.  Sound from
the abyss is (in the absence of passers-by) only an occasional sighing,
as of distant winds, or very distant gales.
  Our scientists have determined that the light we see by, that wells in
the day and wanes in the night, comes from the rock of the wall, and the
air itself near to the wall.  Why it waxes and wanes, and what force can
cause the very air to give out with light, they cannot say.
  Men's houses sit on the wall like the round, dusty hills of the
spider's nests, clinging to the houses' walls.  Roads are hacked into
the rock, winding switchbacked between the houses, through towns, narrow
and crumbling in the wilderness.  Left to itself, the wall face is
irregular, bumpy, with long cracks and clefts, ledges leading to
nowhere, chimneys and hollows.
  The general tendency of each level is to slope inward (toward the
wall) at an angle comprising about one twentieth part of a circle from
the abyssward direction (the direction of the pull of gravity).  At the
border between one level and the next, there is an overhang, so that the
lowest parts of the upper level thrust outward into the void beyond the
upper parts of the lower level, and in fact beyond the lower parts of
the lower level, so that although each level slopes wallward, the
general tendency of the wall as a whole is to jut abyssward.  At least
this is what the legend says, and the dim looming greyness we see
looking up in the daytime, and the evidence of debris and fallers,
supports it.
  Passing from one level to the next lower is thus possible, although
neither easily nor without danger, by the means of long ropes and
pulleys or (if no assistance is to be had on the level below) by
swinging.  Travel in the opposite direction, from lower to higher
levels, is on the other hand all but impossible in the normal course of
things.  The rock of the border overhangs is tough and not subject to
cracks or fissures large enough to permit passage, yet has enough of a
tendency to flake and chip near the point that all efforts to establish
permanent bridges from this level to either of its neighbors have met
with (usually tragic) failure.
  The vertical height of the level varies, being generally between two
and five days travel from lower overhang to upper.  This does not take
into account the twists of our roads; if it were possible to move
directly against gravity, the distance would of course be much shorter.
  Because it is in general possible to cross the boundaries between
levels in only one direction, the general spread of humanity has been
downwards, towards (presumably) Sheol.	The population seems to be
distributed uniformly in the lateral direction (left and right across
the level), but to be spreading slowly downward between levels, as if
humanity had begun somewhere far, far above (and why else would the
levels be numbered, reckoned from up to down).	Strong tradition holds
that when one level becomes too crowded, the dangerous migration down to
the next becomes more common, until the lessening of population due to
bordercrossings (successful and unsuccessful) balances the birthrate.
As our people are never extremely fecund, this desertion rate need not
be high.
  There is some evidence to support popular tradition's picture of human
migration.  The villages near the top of the level tend to be the oldest
and best established, and the density of population there is higher.
   One of the favorite and longest-disputed topics among the
philosophers of this level is the fate of fallers.  Fallers are those
persons, or seeming persons, who pass by the level, more or less far out
in the abyss, on their way from somewhere above to somewhere below.
The popular wisdom states that the fate of fallers is simply to fall,
until they reach the levels of Sheol, and are melted to nothingness.
This is too simple for many of our wisest, however.  They are divided
into several schools.  One set of schools holds that, somewhere between
this level and the deadly nether reaches, there is something that brings
the fallers to a halt.	The schools disagree in the nature and placement
of these obstacles, the purposes of their creators (if any), whether or
not the obstacles are such that the fallers are destroyed upon meeting
them, and a host of other questions.
   One of the more notorious schools of faller theory, popular in our
great-grandfathers' day, held that ten thousand levels down, silken nets
bring the fallers to a gentle halt, and they are led off by servitors
(there was a schism early in the history of this theory on the question
of the gender, if any, of these) to await, in honored opulence, the day
when the normal migration of humanity reaches those regions.  This
school flourished in that time of optimism, but it tapered off as its
most staunch defenders journeyed to the lower edge of the level and
hurled themselves hopefully into space, equipped with greater or smaller
numbers of philosophic texts, missives, and holy runes intended to
ensure their friendly (not to say warm) reception in the Advanced
Regions.