To the south and southwest of Dublin lie the Wicklow Mountains, a largely wild area at the center of County Wicklow that today is preserved as a national park. Buck Mulligan turns toward these "awaking mountains" at the beginning of Telemachus, and Leopold and Molly Bloom both remember a night when they returned in a jaunting car from a dinner at the "Glencree reformatory," passing over the "featherbed mountain" that is part of the range. In Lestrygonians and Penelope the Blooms think of an incident near another County Wicklow mountain called "the Sugarloaf," which is not part of the Wicklow range proper.
Some of the Wicklow Mountains (or the Dublin Mountains, as the northernmost ones are sometimes called) are visible from the top of the Martello tower on which Mulligan and Stephen Dedalus stand at the beginning of Telemachus. In a phenomenon familiar to anyone who lives near mountains or tall buildings, morning sunlight hits the tops of these hills before any of the surrounding countryside, so they seem to be "awaking" first.
The Blooms were in the same mountains at night. They had attended a fund-raising dinner at St. Kevin's Reformatory, a Catholic male reform school located about ten miles away in Glencree, the second closest valley to Dublin. ("Glen" means "valley"; the nearest is called Glencullen.) A car brought the Blooms back to Dublin from this "Glencree reformatory" over the adjacent region called the "featherbed mountain," which is not a peak but simply an area of higher elevation, sometimes called the Featherbed Mountains. From this high, open, and dark country, Bloom pointed out various constellations to the other three people on the car.
The top of the Glencree valley is accessed by the Old Military Road that the British built in the first decade of the 19th century to flush out United Irishmen rebels who were hiding in the hills. A barracks was built there in 1806 but closed down in 1815, and in 1858 the buildings were repurposed as a reform school. The Reformatory closed in 1940. In 1975 it was replaced with the Glencree Centre for Peace and Reconciliation, to promote understanding between Catholics and Protestants in Northern Ireland during the time of The Troubles.
The Blooms' recollections of a picnic at "the Sugarloaf," and another mention in Cyclops, apparently refer to the Great Sugar Loaf or Big Sugar Loaf, a mountain in the eastern part of County Wicklow, just south of Bray. This mountain is even more easily accessible from Dublin.
Ulysses also makes multiple mentions of a reservoir just to the east of the Wicklow Mountains, created in the 1860s by damming the Vartry river. And Bloom recalls a school trip to a waterfall at "Poulaphouca," on the Liffey river to the west of the mountains. That area now holds another, even larger reservoir, built in the 1930s and 40s by damming the Liffey.