The Knowing of Selb-Kar

"The Knowing of Selb-Kar" is the title of this volume of demonological
lore.  

Unfortunately, as is most often the case, the bulk of the tome is actually
the mad ravings of its author, who consistently refers to himself in the
third person, by the rather regal title of "The Grand Hierophant of
Geometry".  

One particularly lucid passage describes a location in the Void known as
"Selb-Kar".  It is unclear whether Selb-Kar is a city, a geographical
feature, or some sort of unholy temple.  

One fairly lucid passage describes a trip the author made to Selb-Kar, and
things he witnessed there:

"Tall spires of angles more obscene than acute shadowed me.  Vershaks
shrieked catcalls above.  There was no light until I saw the Intersection. 
A host, no, a floating, flickering, SENATE of shape met at the Intersection.
Dark, alien polytopes, led sonorous fugues, speaking things that no thing
ought not, for they were no thing.  They turned, and I looked at them, but
they LOOKED BACK.  They CHANGED me, and now I SEE.  

MY SOUL HAS A SHAPE NOW"

The rest of the book is far less coherent.  Towards the end, the author
promises to reveal the arcane "Angles of Selb-Kar" which can be used to
summon denizens from that place.  True to his word, the last page is
inscribed with a complicated and obscure collection of runes, lines, and
angles, denoting the mystical symbol referred to be studied by the skilled
scholar.