When Stephen thinks "I am here" at the beginning of Proteus, he is standing somewhere on "Sandymount strand," the beach and tide flats east of the suburb of Sandymount on Dublin's southeast periphery. The action of Nausicaa takes place on the same stretch of shoreline. And both episodes of Ulysses invite comparison with the passage at the end of Part IV of A Portrait of the Artist in which Stephen walks along a beach on the north side of the Liffey, near Dollymount.
Between the end of Nestor and the beginning of Proteus, Stephen has moved from Mr. Deasy's school in Dalkey, south of the tower at Sandycove, to Sandymount strand northwest of the tower. The novel does not represent that journey or give any hints as to how it may have happened. Did Stephen walk the whole way, or take public transportation? In James Joyce's Dublin: A Topographical Guide to the Dublin of Ulysses (Thames & Hudson, 2004), Ian Gunn and Clive Hart infer that Stephen must have caught the 10:00 train from Bray at Dalkey Station, at 10:10, arriving at Westland Row Station in the city at 10:42 and then walking east along Great Brunswick Street towards the strand (28-31).
The Sandymount strand opens onto a vast tidal flat that becomes exposed at every ebb tide, allowing walkers to venture far out from the land. After venturing a short distance onto these flats, Stephen heads in the direction of the South Wall, spends some time there, and then journeys toward Dublin, where he will spend the rest of the day. (This last action, like the passage from Dalkey to Sandymount, is not represented in the novel. We next meet Stephen in the newspaper office on Prince's Street in the center of Dublin. Has he walked the whole way, or caught a tram for some part of it?)
In Nausicaa, the novel returns to "the weedgrown rocks along Sandymount shore," to find Gerty MacDowell and her companions (and, soon, Leopold Bloom) sitting in a spot not very far from where Stephen began walking at the beginning of Proteus. Nausicaa begins shortly after low tide, but the characters in this episode remain close to shore: nighttime is fast approaching, and they have young children with them.
In Part IV of A Portrait Stephen walks near the North or Bull Wall that juts out into the sea from Clontarf. A young woman who is wading in the water there accepts "the worship of his eyes" much as Gerty MacDowell accepts Bloom's. Like Gerty her wearing of "slateblue skirts" may associate her with the Blessed Virgin, while "the white fringes of her drawers" excite desire. Both encounters (the one in Nausicaa more strongly sexualized) should be read in the context of Joyce's experience with Nora on the Sandymount strand, an experience that Stephen anticipates in Proteus when he thinks, "Touch me. Soft eyes. Soft soft soft hand."