* '''Ciutadella park''' is closed at night, but may be accessed by the entrance facing the Arc de Triomf. The bars of the fence near the gate are wide enough to slip through if you're not very big. You're unlikely to be disturbed during the night but the Police might wake you up after 8am and ask you to move on. Another user got inside and pitched a tent. It is safer if you are not alone. Lot of criminals and junkies also sleep there dont talk and dont trust anyone. Attach your bag to tree with rope when you sleep.
*Small park just '''in front of the Cosmo Caixa''' Museum where you can easy use a tent. By public transport, you can get the L7 to the end ''Av. Tibidabo'', than walk 5 minutes direction top of the hill, turn on the ''Carrer d'Isaac Newton'' just before the bridge on the left and continue. You will find this huge building, with a big submarine in front of it. When you have museum on your back, submarine on your right, there is some [http://goo.gl/maps/MxfX2 stairs] in front of you, between entrance of museum and submarine, you will see the main door of this park after few stairs, it might be close if its late, so you can go to the top of this stairs, than jump on the left side, go under the stairs to the other side, and there is the spot. 2 options: (1) near the bench, better for the ground, but you might be visible at the morning, and woke up by a guardian; (2) right after geting out from under the stairs, the ground is shitty, you might need good stake to setup your tent, mostly in windy time, from there, the guy who open the door at the morning, can't see you, and he don't go into the park at all, so you can sleep till late!
*Take the metro from "Placa de Catalunya" to '''Canyelles station''', walk about 200 yards uphill from the station and find some nice hills to camp/sleep out/hang a hammock. You can meet wild boars
*Take a late train to the park in the North-West of Barcelona. For example, you can take the S2 to ''Sabadell'' (ticket zone 1) leaving from ''Plaça de Catalunya'' and getting off at ''Baixador de Vallvidrera'': there is a big park which is nearly like a forest, and you will find a very good and lonesome place to stay within 500 meters from the station.
*'''Parc de la Pau''' - small and clean park next to the beatch (15 min from metro to station Besos Mar, next to Dechatlon shop, street Career de la Pau)...
*With tent you can try to camp next to '''Camp De Futbol Canyelles''' (metro Valldaura and next to Institut Escola artístic Oriol Martorel, street Camí Antic de Sant Llàtzer)