Also a good short novel by
Lawrence Durrell.
There is a book on the subject by a Catholic scholar,
The Legend of Pope Joan: in search of the truth
by Peter Stanford (Holt, 1999). Stanford is a serious
scholar who set out to debunk the "legend" once and
for all, but ended up believing that it was true.
One review says, "Unable to prove conclusively that Joan and her papacy existed, he is nevertheless able to present a remarkably credible and convincing case on her behalf."
Since he is a published and reputable pro-RC scholar, he was given
access to many Vatican documents and artifacts, and
claims to have seen and sat in the chair described above, and he described how it was different
from the below-mentioned "Roman toilet".
And btw, perhaps Segnbora-t recalls Benedict III
coming quickly up the stairs, but I was not around back
then, so I can't be as sure.