You can visit the most popular monuments in the city being maximized your time. Proposal:

-The Gaudi Tour, includes entrance to Sagrada Família and Park Güell (and no queues)
-The Montjuïc Hill and Waterfront Tour, spectacular views over the city.
-All Barcelona Highlights Tour, the ideal tour to cover the very best of Barcelona in a day
-The Montserrat Tour includes entrance to audiovisual exhibition.

Specialized guides, competitive prices, book online, private tours … and quality guaranteed with Barcelona Guide Bureau. (+)