The River Liffey is diving Dublin in two, but the two parts are still connected with several bridges, some for traffic and walking, while others are only available for people on foot. A nice way to get to know Dublin better is to travel on a river cruise. On such a cruise you get to see the city from the river, and on some tours you will also have a guide on-board giving you information about what you see. Some tours are available with food, drinks and it is also possible for companies to rent private boats for special occasions.
The river cruise in Dublin can not be compared with river cruises in for example Budapest and Prague, but it is still a nice activity for those interested.