Most of Dublin’s tourist attractions can be reached on foot, but if you do not have to much time to spend in Dublin a City Tour by bus might be an alternative.
There are a couple of bus companies you can choose from, and they can be found along O'Connell Street.
They leave every 10-15 minutes. You can hop on and off at any of the stops around the city and continue on with the next bus. The tour lasts about 1 hour 20 minutes and a ticket costs around 12 euro.
I didn't take the bus because I had plenty of time in Dublin, but I think it is a good alternative if you dont have too much time or if you feel too lazy to walk.