The mention of "the steps from Leahy's terrace" fixes
Stephen's location at the beginning of Proteus
fairly precisely, and also links him with the location of
Bloom in Nausicaa. Leahy's Terrace is a road in the
eastern suburb of Sandymount.
It runs southwest to northeast, beginning at Sandymount Road
and terminating, at the time of the novel, at a seawall
bordering Sandymount Strand. (Since that time, land has been
reclaimed from the sea, pushing the seacoast further east.)
Stephen is walking on the sands exposed by the ebb tide and
sees two women coming down the steps from the road to the
beach. The Star of the Sea
Church that focuses the action in Nausicaa is
also sited on Leahy's Terrace, very near the water. It seems
certain, then, that Bloom and Gerty MacDowell cannot be seated
far from where Stephen is walking when he sees the two old
women descend the steps for their walk on the beach.
The steps that Stephen looks at no longer exist, and their
former location is a matter for detective work. In 1960,
before the Irishtown
reclamation project, William York Tindall published a
photograph of steps that he assumed were the ones mentioned in
the book, and Clive Hart and Ian Gunn reproduced his image in
their James Joyce's Dublin (2004). But they have
discovered more recently that a smaller section of the strand
was reclaimed in the 1920s, meaning that Joyce's steps must
have been located still farther west, closer to the church.
See Gunn's short article in James Joyce Online Notes.