We have not made an exhaustive visitor's guide because Barcelona is so popular and most things we could think to say have already been said better by someone on the Internet. However, we will make a few recommendations here, mainly related to things that are noteworthy for their proximity to the ESSLLI site or because we think we can provide some added informational value.
Printing/Photocopying: In addition to the printing/photocopying facilities in the UPF Library (about which see ESSLLI booklet distributed at registration), you can go to 4 Colors on Rambla de Poblenou, 117-121 (10-14h, 16.30-20.30), Copisteria TPI on c/Marià Aguiló, 92 (9-14h), or (a bit further away, but between Onix and the UPF Campus) Copiservei on c/Pamplona, 48 (9-14h, 16-19.30h).
About the ESSLLI neighborhood: UPF's Poblenou campus is part of the Poblenou Urban District, Barcelona's area for creative arts and technologies. There's lots of stuff going on in the neighborhood (though perhaps things are a bit quieter during August). For information about Poblenou Urban District, including restaurants, bars, stores, and activities, check out: http://www.poblenouurbandistrict.com/en/.
Beaches: There are beaches all along almost all of the waterfront. Bogetall beach tends to be somewhat less crowded than the others; the Nova Icària beach tends to be quite crowded. Note that the Mar Bella beach allows nude bathing. All municipal beaches are monitored for the safety of the current using a green/yellow/red flag system, as well as for the presence of jellyfish, which can sting. To find out the current state of the beaches, you can check out this web page (app also available): http://interior.gencat.cat/.content/home/030_arees_dactuacio/proteccio_c...
General guide to going out in the city: Time Out Barcleona, http://www.timeout.com/barcelona
Rollerblade rental: Rollerblading on the beachfront is an excellent way to take a break from ESSLLI. You can rent roller blades on an hourly basis at various places. Here are a few:
http://www.inercia.com/es/alquiler-de-patines (about 10 min. walk from Onix)
Indoor Rock climbing: There is a place called "Deu dits" (Carrer de Pamplona, 106), www.deudits.com
Bicing (the public bicycle), and biking: Unfortunately, you cannot use Bicing unless you have an annual subscription. There are many bike rental shops around Barcelona, including in Poblenou. If you rent, you should be sure to have a good lock and always lock well, as theft is an issue. We do not have any particular bike rental recommendations, but note that one of our excursion options is precisely a bike tour.
Cinema in original version:
Verdi Cinemas, c/Verdi, 32 and c/Torrijos, 49 (Gràcia neighborhood): http://www.cines-verdi.com/barcelona/
Yelmo Icaria, "El Centro de la Vila" shopping mall, Av. Icaria, 160: http://www.yelmocines.es/
Filmoteca de Catalunya, Plaça Salvador Seguí, 1–9 (Raval neighborhood): http://www.filmoteca.cat/web/
Mèlies, c/Villaroel, 102 (Eixample Esquerra neighborhood): http://www.meliescinemes.com/
Museums/Monuments: There are so many tourists in Barcelona that we strongly recommend that you plan in advance any visit to a major tourist site, such as the Sagrada Família, the FC Barcelona museum, or Park Güell. Many sites (including these) sell tickets on line with specific visit times that can fill up several days in advance. For those of you who visited Barcelona in the past and have not been here recently, you should be aware that many places that were once freely accessible (such as the Cathedral or Park Güell) now charge an entrance fee.
Food shopping: If you're staying at Onix, we recommend that you check out the Fort Pienc municipal market in the same building (entrance on c/Ali Bei, just around the corner to the right). It's open 8-15h every day except Sunday. The quality-price ratio is very good. Louise's favorites: The veggie stand just next to the c/Ali Bei entrance, Solé & Fills for fish (note: Monday is a bad day to buy fish), and "Aviram i derivats Piñero" for poultry and meat.
If you're staying at Urbany, the closest municipal market is the Mercat Municipal del Clot. The pedestrian area around this market has many little stores with good products for not hugely expensive prices. If don't mind non-organic produce, a very good option is any Sorli Discau grocery store. Sorli is a local chain, started in Poblenou. The prices are on the low side, the produce is generally ripe, varied, and of good quality, and they have a good variety of other products. There are Sorlis near Urbany (c/Mallorca, 590) and Onix (c/Casp, 143), and elsewhere as well. If you really want organic food, there is a fairly complete organic food store, Veritas, in the Glòries shopping mall. For those of you who know Whole Foods, Veritas is the Whole Foods of Catalonia. It's not particularly cheap and not particularly recommendable. If you wander around the Rambla de Poblenou and the adjoining streets (especially Marià Aguiló and the streets around the Poblenou Municipal Market), you'll find a few other places. If you're on a very tight budget, the Mercadona grocery store in the Fort Pienc market and the Carrefour in the Glòries shopping mall are good options. There is also a Lidl on c/Pujades 15-17. If you like wine, it's very easy to find very good wine for less than 10€, sometimes even less than 5€/bottle. Don't feel obliged to spend a lot.
Restaurants: There are too many to recommend, and too many of you. Our only advice is to avoid places that look like they cater primarily to tourists (one dead giveaway is a sign advertising paella). In general, restaurants offer fixed-price menus for lunch which are around 10€ for two courses plus dessert and a drink. Some places allow you to order just one course+dessert and a drink for slightly less. If you order a full menu, you can always choose two first courses instead of one first and one second. If you just want a sandwich at midday, bakeries and bars often have sandwiches for sale or will make one to order.
Restaurant hours: It is increasingly easier to get food at European hours, but your options are going to be limited before 1pm for lunch and 8pm for dinner.