Josie Breen tells Bloom in Lestrygonians that Mina Purefoy is in her third day of labor at "the lying-in hospital in Holles street." In Oxen of the Sun Bloom shows up at this hospital, whose location is announced in the episode's opening sentence: "Deshil Holles Eamus." The action of the chapter takes place, we hear later in the chapter, "in the commons' hall of the National Maternity Hospital, 29, 30 and 31 Holles street."
The hospital is in southeast Dublin just north of the Merrion Square park, a location that is highlighted as the chapter describes a rainstorm moving in: "In Ely place, Baggot street, Duke's lawn, thence through Merrion green up to Holles street a swash of water flowing that was before bonedry." The sentence describes a storm track moving roughly from southwest to northeast.
In Ithaca, when Bloom and Stephen discuss places to continue their conversations at later dates, one place suggested is the site of their first conversation: "the National Maternity Hospital, 29, 30 and 31 Holles street."
The National Maternity Hospital was founded in 1894, and is currently one of three maternity hospitals in Dublin. So many babies are delivered there each year that a move to larger premises is being explored.