Sandymount Strand is where Dublin runs out into its bay — a tidal flat so vast that at low water the sea pulls back half a mile and leaves a hard mirror of wet sand under the Poolbeg chimneys. It is also the most literary beach in the world: Stephen Dedalus walks it in Ulysses, eyes shut, "the ineluctable modality of the visible". An afternoon walk, entirely flat, and ruled by the tide — check the timetable before the train timetable.
Start at Sandymount Green and the Martello tower, then out onto the strand at low water, walking the firm sand toward the channel with the striped chimneys ahead. Don't overreach: the tide returns fast and level across the flats. Come back in by Irishtown Nature Park, green over reclaimed ground.
If the light holds, the Great South Wall runs two kilometres out to the Poolbeg Lighthouse — exposed granite, the best evening walk in the city, though it sits beyond the chimneys off the main line. Otherwise follow the seafront back, Wicklow low to the south, and cut in to the DART at Lansdowne Road.