We'd like to add our recommendation for Spain Day Tours, as well. We went on the "Best of Barcelona Guided Tour with Port or Hotel pick-up". It's a half-day tour. Before the tour, communication from Spain Tours was excellent - tickets were purchased for us to visit Park Guell and we were sent a full itinerary of what we'd be seeing. We were collected right outside our ship by Tony in a smart 6/7-seater people carrier. He was exactly on time, 8.15am. We picked up a family of four from another ship and Tony organised our schedule to avoid the worst of Barcelona's traffic. He was very knowledgeable and cheerful. If you want a rapid introduction to the best sights of Barcelona in half a day, this is the tour to go for.