I visited several beaches in and near Barcelona recently. Here are my reviews:

El Prat Nudist Beach

This can be reached on the PR3 bus from El Prat de Llobregat station, which is one stop from the airport on the airport railway line. The bus ride takes about half an hour. When you get off, walk to the left past the sailing club and over a bridge to discover a fantastic 150 metre long naturist beach, with singles, couples, friends, families, and it would seem, all locals. There's a beach shower as well. It's my favourite beach in the Barcelona area, whatever the day of the week.

Mar Bella Nudist Section, Barcelona.

The southern end of Mar Bella (a beach in Barcelona, not the town in southern Spain) is designated as nudist, but there are a lot of costumed people here, especially on a weekend. The beach is clearly a favourite of the gay and lesbian community and I was surprised how many couples and groups had only one or two going naturist with the other(s) costumed. From reading stories on here I would have expected the majority of people who go to nude beaches with naturists to eventually become ones themselves, but obviously that's not the case. Beach showers here too, but also lots of fully clothed people wandering past. This beach is OK to steal an hour at, but not a destination otherwise. Not especially easy to get to by public transport either. Poblenou metro stop is 15 minutes away.

Playa de la Mora, Sant Adria de Besos, to the north of Barcelona city.

I have seen this beach referred to as Chernobil, and it's easy to see why. Get a tram or train to Sant Adria de Besos and walk parallel to the railway line keeping the power station towers to your right until the power station  is mostly behind you. Then turn right and approach the sea.

I have never seen a naturist beach with a demographic like this. When I arrived the half nearer the power station was clearly the gay half. But as the beach filled up that became less clear as people went wherever there was a space. When I arrived, the other half of the beach was almost exclusively older mixed sex couples, and most of the women were wearing bottoms. A few twentysomethings did show up. But a noticeable lack of people aged 30-50.

Again, worth stopping here for a bit if you're near but there are better places to go.

Musclera Beach, Arenys de Mar

The railway line extends from Sant Adria de Besos up the coast. I saw a few nudists from the train, the line is that close to the beach. My destination was Musclera, which is fifteen minutes walk further on from Caldes d'Estrac station. The first thing to note is that the railway line goes straight past this beach and there are trains every ten minutes each way at peak times. Given this nude beach extends for 500 metres and we were five rows deep, it didn't bother me at all. Returning midweek instead of Sunday, I found we each had 30 metres length of beach to ourselves. Great in some places in the world, but with the frequent trains it felt a bit odd.

A great beach, but go on a Sunday like the locals do to feel the community spirit.  Beach shower, and (clothed) beach bars as well. A fantastic mix of people.

Coves, between Sant Pol de Mar and Calella

There are several coves just south of Calella. Looking on the Internet I don't think I even got as far as the main nude area, but the cove I found was simply beautiful. If you come here expect to see several groups (who must have traversed the whole of the beach to the left) come upon it and realise this beach was not quite what they expected. Also the only time I heard English spoken around me, two topless Australian women with their nude Spanish friends.