If you do not want to go far outside of Barcelona, to swim in the sea and soak up the sun, advised to 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, It is known because of its shape in the form of sails. Here is a segment for nudists, so it is not surprising abundance of absolutely naked bodies. If desired, you can also completely undress, just do not go out in this video outside the beach, to wash in the shower, also throw with trunks or a swimsuit, otherwise the police may have to reprove.
Water on the beach of San Sebastian is much cleaner, than Barceloneta, here formed smooth bight, 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, about which the pensioners playing paddle, something like tennis on the Catalan way.