The regular, and ever-popular, Flea Market is taking place in a new venue this month, and the organisers will be praying for a sunny day, as it's being held in the great outdoors.
Head to Plaça Blanquerna in Raval (between Drassanes and Avinguda Paral·lel) to find second-hand clothes, books, records, accessories as well as a few knick-knacks.
If you'd rather be a seller than a buyer, no problem. Just send a mail to firstname.lastname@example.org telling them what kind of things you'd like to sell (has to be second-hand, no manufactured or hand-crafted stuff), and they'll get back to you to let you know whether you've got yourself a stall. Just a word of warning, this special outdoor event is a bit more pricey than the normal Flea Market, so having a stall will cost €20 (although they can be shared, and you do get a possible suntan thrown in; just don't forget your suncream, or it'll be guaranteed sunburn).