Having given tours of Grand Central Terminal across the glass floors
of the end window-walls of the Main Concourse, I've found that 80 out
of 100 love the experience, 19 out of 100 are a bit uneasy at first
but move right ahead, but 1 out of 100 can't take it.  One woman came
close to hysteria and nearly had to be drugged to get her out of the
area.
I would like to consider the glass floor solution elsewhere, gaining
the glow of light streaming through walkways.  The hysteria issue
aside, I would like to know if there is source to glass floor systems
still available.  Anyone know of any...old style, restoration or new?
The sidewalk vault round-glass-insert-in-concrete solution was also
used by architect Ernest Flagg as skylights over the oculus of the US
Naval Academy Chapel in Annapolis.  I documented it, but they were
removed due to leaking and subsequent mutilation, replaced with
contemporary skylights worked discretely into the copper dome.

--Jim

P.S.
My earlier reply to the glacier glass issue seems to have disappeared
into the ether, wherein I speculated that the reference was to
glue-chipped glass whereby tenacious glue is applied to clear glass
which upon drying rips the glass surface off into beautiful Jack
Frost patterns.  This technique was used at least by the turn of the
century, I believe, and is still available.  (My 2 cents worth.)