If you do not want to go far outside of Barcelona, to swim in the sea and sunbathing, we recommend you go to the beach San Sebastián, which is adjacent to the beach of Barceloneta, but at the same time completely different from him.
It's the nearest beach to the hotel W, well-known because of its shape in the form of a sail. Here is a segment for nudists, so it is not surprising abundance of absolutely naked bodies. If desired, you can also completely naked, just do not go out in this video outside the beach to wash in the shower, too, melt fling or a swimsuit, or the police may have to reprove.
Water on the beach of San Sebastian is much cleaner than in the Barceloneta, here it forms a smooth bay, where it is always clean and bright. The people here, too, an order of magnitude smaller.
Opposite the beach there is a water sports club with a lot of pools, some of which pensioners playing paddle, something like tennis on the Catalan way.