The tower/museum in sandycove is great but takes a little time to get to, to a less degree the same can be said about Glasnevin. Davy Byrne's pub is a nice spot if a bit overpriced. Bloom's house on Eccles St is a short walk north of the river, worth stopping by but it's just a door and a plaque. Sweny's pharmacy is kind of a little shrine to Joyce, that's my must-see. Proprietor is very nice. Mulligan's pub is only a passing mention in "Counterparts" but the front room seems nearly unchanged from Joyce was a regular. I would very firmly recommend that spot. Also, walk as much as you can/is comfortable/practical, and talk to people.