There's slightly more to Barcelona than paella and Gaudi.
In case you didn't read the guide book (or you only got a cheesy one for tourists) here's a super-quick antitourism rundown of what's actually good to see in Spain's capital city.
La Rambla and the Port
Walk along a racing line from Plaça de Catalunya to the port in as little time as possible. There are three photos worth taking. One of the wide pedestrian-packed boulevard, the second of the amusing real life mannequins and the third of the petty criminals as they steal your wallet. You'll see them trying trick you into a ball-cup gamble. Too late. He's gone.
Impressive due to it's monstrous volume of fresh produce, La Boqueria is ironically the biggest market you'll ever go to and probably come away with nothing.
You'll be completist, you'll wander ever aisle and reach every corner. You'll see beautiful displays of fresh seafood, vegetables, regional delicacies. You'll buy a filo pasty shaped like a cumberland sausage it will be good but fleeting. If you've still got your wallet, splurge on a fresh juice from one of the 55 vendors.
The Beach and Barceloneta
Barcelona beach is on the best sea in the world; the Mediterranean. Good sand, warm waters an island to swim to and it's proximity to the city are enough to make everybody jealous.
Trumping all of this are the neighbouring streets of La Barceloneta. These tight streets of residential blocks are oozing layers of repression and gentrification. If I lived in Barcelona I would live here. Every day I would walk down to my corner deli-bar, drink a clara and argue with the locals about unemployment.
East of La Rambla are a network of painfully picturesque alleys and plazas. The more lost you get, the fewer tourists you'll see so make this a priority. Look out for artisan garages, neighbourhood bars curious galleries and upmarket plaza refits. Have a bottle of water to hand and stay hydrated.
Agbar Tower and Santa Caterina Market
Barcelona is only 95% Gaudi. Of the newer projects a couple stand out. From afar, Torre Agbar is a ginormous monet-wrapped bullet, glistening in hues of red and blue in the long afternoon sun. Impressive at a distance, it reveals it's budget construction up close... like a poor-man's Swiss Re.
Like a Marylebone Waitrose, you just know the peaceful layout and beautiful produce at Mercat Santa Caterina are going to attract a hefty premium. Come here instead for the roof, an undulating technicolor timber tapestry. You'll not be able to wangle you're way up there but the surrounding buildings offer a vantage point.
(also worthy of a runner's up prize is Richard Roger's Bullring. For some reason they lifted the entire bullring up a few inches and turned it into a mall)
La Sagrada Familia
Only an imbecile would visit Barcelona without going to the Sagrada Familia. Find out why in my post on Gaudi's masterpiece Cathedral.