Although we visited Barcelona outside the main season (at the end of January) the Bus Turistic service on both routes open (red and blue) was still very frequent and the multi-language commentary on the supplied headphones very informative (you may prefer to take your own in-ear headphones as the free ones supplied, although functional, were not the most comfortable for a two hour trip). The two routes cover all the main areas and attractions of the city and provide an excellent sense of the geography of the city as well as great views from the open top upper deck. Wrap up warm in cool weather though, it does get draughty up there and when it rains it does blow in under the sliding convertible roof! Booking online in advance saves a worthwhile amount on the cost (we had two day tickets) and we were very happy we chose this activity as we were able to see a good deal in just a couple of days. It's best to make an early start, and if you stay out to eat in the evening remember the last buses set off at 7.00 in the winter and 8.00 in summer so you may need to get back by metro. Definitely a worthwhile option if you are not already familiar with this wonderful city.