When I went to Spain I brought two with me from the libraries, the DK Eyewitness Top 10 2017 Barcelona and Lonely Planet's Best of Barcelona that was fresh off the new books shelf. Both were interesting but I was almost overwhelmed with the places and things to do. I was also a little stymied by the fact that neither of them fit in my handbag (my fault), but the suggestions weren't very useful for someone with only 2.5 days in the city. The Sagrada Familia may be a "must see" but the queues are insane. The Hospital de la Santa Creu i de Sant Pau is a well worth the trip, under touristed space where we had space to wander and a great time (I also spent too much in the gift shop).
To be honest they were good but quick googling helped us almost more.