More and more cities are using double-decker buses with open tops (London style).
Barcelona has two different routes. The fare is about 15 Euros for the whole day and the route map gives the main tourist sights. They are hop-on, hop-off buses. Ear pieces state the route and stops in various languages.
We spent an entire day and did not have time to see as much as we wanted. We were spoilt for choice !! No need for a guide. We will be there, again, in mid Sept.and see what we missed.