90 minute tour took us to the 23 major sites in Dublin. Then we had a better idea of which spots we would visit for more inspection. Best time spent were St Patrick's and Guinness Brewery. Very easy to use and busses were every 15 minutes or so.
We have found these bus tours excellent value in other large European cities and Barcelona was no different. We were centrally located and caught the first bus (9.00 am) at the main square. Later in the day we noticed very long queues in the hot August sun but not sure how long it took to board the bus. I would recommend this tour especially if you need to rest your feet!