You cannot appeciate nor explain Barcelona without talking about Gaudi.  You can walk into the Segrada Familia and take thousands of photos while you are in awe.  Then you make your way to Guell Parc and see the extension of his reverence for nature. Beyond that, walking Las Ramblas and experiencing the artists who dedicate hours of remarkable entertainment, restaurants who serve amazing paella, and wonderful little pubs make any day relaxing and enjoyable.