The Martello tower at Sandycove stands on a cliff overlooking the Forty Foot (check the Forty Foot article), and was immortalised in the opening scenes of Joyce’s ‘Ulysses’. James Joyce himself stayed there for six days before being scared off by a gun-toting Oliver St. John Gogarty (another Irish literary legend). The Tower is one of a series built along the Dublin coast to protect against a potential French invasion in the 19th Century.
It’s now been converted to a small museum dedicated to James Joyce, which is free to visit. The museum itself is quite petite, just three rooms with Joycean paraphernalia, and one converted to look as it would have when Joyce stayed there. The real draw is the roof, from which you can get views across Dublin bay. A visit would take less than half an hour, but you could combine it with a swim, a visit to Finnegans in Dalkey, or a browse through the People’s Park Market in Dun Laoghaire.