I was there for 9 or 10 days back in May. Tons of different stuff to do, depending on what you are interested in.
Below is an email a friend wrote, she may sound a little young and childish but she is actually a very attractive doctor in LA. It may take a little deciphering but all of her suggestions were awesome.
Hey dude,
Ok so- I just looked it up, CHUPITOS still exists on Paseig de Colon (on the water) but it looks like it's had a bit of a revamping and may not be quite as old and rustic as i remember, but you should def check it out nonetheless.
Also- right inside the entrance to the wax museum at the end of Las Ramblas by the Cristopher Colombus statue there is a bar that literally looks like you are walking into a forest. It has the bombest sangria. You literally find the entrance to the wax museum, and turn right once you walk through the gate. Make the trek down Las Ramblas during the day and at night, but this is where tourists get jacked so watch your shit and put your wallet in your front pocket. Right off of Las Ramblas is (to the left if you are walking towards the water) is Plaza Real, which is a sweet hangout at night. We used to get wasted and sit on the fountain there and meet people. My favorite restaurant is in Plaza Real, the best food with the best price (and the best gazpacho!!) It's called Les quince nietz or something like that, you should see it if it's still there. Also, when you are walking down Las Ramblas towards the water, off to the right is another open square called Rambla Raval, and there was a very dangerous authentic absinthe bar there in the corner. Try and find this. I was once licked by a homeless man while chain smoking outside and I wasn't phased at all. It's excellent.
Another MUST is to go down to the beach, lay out, smoke hash (there are dudes walking by selling it constantly, along with cola and beer) and drink sangria. The whole beach area was redone for the olympics and i remember it being pretty nice. There are also a lot of restaurants down there but they are very touristy. Don't worry, if you happen to drunkenly fall on a broken champagne bottle in the baja beach club, the most touristy college beloved patriot joint on that strip, the Hospital del Mar is close by lol.
ALSO down by the beach is a sushi joint called Shoko that is very hip and gets pretty hoppin at nights. Facing the water, if you walk to the left direction from Shoko you'll see Catwalk, another club (I remember the dancers being smokin') and even further is left is Port Olimpic, which is about 20 bars/clubs crammed into a three block stretch down on the water. This place is kinda touristy but it just gets fuckin nuts down there sometimes.
Another super euro club place is Otto Zutz. I've had many a 5 am stumbling out of that place. Good times, and you might catch a glimpse of some of the FC Barca players there. I saw Ronaldinho back in the day and almost peed myself.
OK sightseeing stuff. YOu MUST go see La Sagrada Familia, and you MUST take the escalator up to Parc Guell during the day. both are designed by Antoni Gaudi, along with La Pedrera and Casa Battilo on Paseig de Gracia, which is also a cool but very busy street to walk down and a nice place to go shopping.
You can take the subway everywhere just be careful with your shit, pickpocketing, etc is worse than NYC there. Dudes will grab your shit and jump out of the train as the doors are closing. ALSO- DON"t fall asleep on the subway because it goes into a dark tunnel at the end that is difficult to get out of.
Keep in mind that I lived in BCN in 2006. There are probably a bunch of cool new places to go to, but the best thing to do is sit at a table outisde and eat dinner in the street and drink wine and watch people, which you can do anywhere.
OMG I almost forgot. MAKE SURE you go down to the Ciudad Vieja. It's only pedestrians, tiny little alleys and hidden restaurants, bars, also a Picasso museum that has a bunch of his early stuff includining an entire room of Velasquez's Las Meninas broken down into cubism. AND the old Cathedral down there is beautiful as well. On Sundays outside of the cathedral in the morning you will see a bunch of old people dancing around in circles, it's called the Saldana I think and it's pretty interesting to catch that. You'll see that BCN is half Catalan half spanish, and a lot of people really just identify with Catalunya and not Spain, which is a totally diffferent culture with it's own language. I really enjoyed talking to rando cab drivers about their opinions on Catalunya separating from Spain which is always a very interesting little chat. Also down in the Ciudad VIeja is the old ROman city, like 2000 years old. It's completely underground but you can walk above it and look down. There still exists a humongous old column from the Roman city, they didn't even realize how old it was until recently and built all of these apartments around it. It's on Calle Paradis I believe.
OK I hope this helps. Just make sure you see some of Gaudi's shit because it's beautiful. And get drunk.
Here is another email I got from a co-worker in our Spain office:
The list of musts, Ill leave the night live to Jordi.
1: Sagrada familia, go and enjoy one whole morning:
http://en.wikipedia.org/wiki/Sagrada_Família
2: Parque Güell, Better during evening, but beside the park I don remember anything interesting around it:
http://en.wikipedia.org/wiki/Park_Güell
3: la pedrera, is in the peso de gracia, visit it till the roof:
http://en.wikipedia.org/wiki/Casa_Milà
4. Paseig de Gracia and Las Ramblas
. Keep an eye on your wallet  (always, but specially
😛)
5: Old town and cathedral. Good example of Gothic Arch.
http://en.wikipedia.org/wiki/Cathedral_of_Santa_Eulalia
6: Estacion de Francia, One of the oldest and most beautiful stations in spain. Its close to the sea an beaches, have a coffee take a look and thats it.
http://en.wikipedia.org/wiki/Barcelona_Estació_de_França
7: Barcelona Pavilion, Mies. It is one of the most beautiful buildings ever. My favorite around the world. Tons of people go to BCN and miss this jewel.
http://en.wikipedia.org/wiki/Barcelona_Pavilion
You can pass all the day in the zone and visit all aroung montjuic:
http://es.wikipedia.org/wiki/Montjuic_(Barcelona)
The Olympic town and the Museo Nacional de Arte de Cataluña
http://en.wikipedia.org/wiki/Montjuïc
And if you are architecture fan you can to go Monte collresola and enjoy the tower and the views, but not much to do around it and is hard to reach it.
http://en.wikipedia.org/wiki/Torre_de_Collserola