It's Catalonia.

This map used to be on naturisme.cat, the Catalan organisation for naturism and would be my starting point.

https://maps.google.es/maps/ms%3Fie%3DUTF8%26hl%3Des%26msa%3D0%26msid%3D115612960045883886575.0000011261d88338019ce%26ll%3D41.652393&ved=2ahUKEwiasejthurmAhV5SBUIHZjkAxkQFjAPegQIAhAB&usg=AOvVaw3qKVlGhMkksfhTaZgMQSU Q"> https://www.google.com/url?sa=t&source=web&rct=j&url=https://maps.google.es/maps/ms%3Fie%3DUTF8%26hl%3Des%26msa%3D0%26msid%3D115612960045883886575.0000011261d88338019ce%26ll%3D41.652393&ved=2ahUKEwiasejthurmAhV5SBUIHZjkAxkQFjAPegQIAhAB&usg=AOvVaw3qKVlGhMkksfhTaZgMQSUQ

Platja del Torn is the closest traditional beach for naturism and the one I would recommend.

I'm guessing they must be doing an update on naturisme.cat website.

I live close to the Ebro Delta and it is a beautiful place in the right seasons, basically Spring and Summer when the landscape is green with the rice crop and golden in early Autumn when the crop is right.  My favourite beach is the Playa Trabajador with the naturist area being at the very end of a long sand causeway but beware of August, the traditional Spanish holiday period when either side of the causeway will be packed with caravans, campervans, moile homes and awnings.  The rest of the year the causeway will be less busy with plenty of room for you to go naked whilst your wife keeps her cossie on.  There are other naturist beaches but they tend to be nearer more busy areas although it is not an offence to go naked on a beach in Spain unless particularly specified.  If there are any particular questions that you would like answered then please to not hesitate to pm me.  I will add that the birdlife on the Delta is of great interest to many, with marsh harriers, flamingoes, heron, ibis and other waterfowl,

Platja del torn is out of the question as it is too naturist orientated and I know my wife won't enjoy it.

Tony, thanks for the advice regarding the August period. So far, and I've yet to sold the idea to my wife in targeting riumar.... Can you tell me more regarding the mosquitoes during July/August? I've read a few things indicating that it can be an issue. If I make a parallel with the French camargue area I guess it can actually be something to account for

Vince, as with anywhere hot and where there is water mosquitoes can be a problem but as the water is not stagnant I can honestly say that I have never been troubled with them.  With regard to Riumar it is a nice spot but can be quiet with many places closed out of season, and I have sun-bathed naked on the beaches there.  Personally I would say look at St. Carles de la Rapita at the south-west of the Delta which has much more to offer and travel onto the Delta as and when you want to. 
Regarding El Torn, it is a fantastic beach and I go there at least once a week when the sun has started to give us some warmer weather, however, there are other naturist beaches between there and the Delta. 

Thank you Tony. I'll have a look a st Charles de la rapita. Looks promising! ;D

Vince, also on the north-eastern side of the Delta there is L'Ampolla which has its own naturist section at the Delta end of the Arenal Beach.  The trouble with that beach is that there is a track behind it which goes through waterbird section of the natural park and can get busy with walkers.  St Carles does not, to my knowledge, have any naturist areas.

I'm not actually looking for naturist beaches as my wife is not naturist but more looking for places where I can go naked amongst other beachgoers without troubles. I understand Spain beaches are pretty open, unless stated otherwise, and as far as I can read it looks like most of the beaches on the delta are open to naturism to different extent. Mostly because they're very big open places with not that many people even during summer months.
I'll see if I can sell the idea to my wife, she would rather go to Italia like last summer because she speaks some Italian but no Spanish at all, like me. Italia is too much of a drive and not enough open to naturism for me. When Barcelona is only 4 hours from home.

From all your posts Tony I can only envy your way of life...

As an alternative holiday with the naturist/textile mix you need I would suggest El Cotillo on the island of Fuerteventura. The beaches there are all clothing optional with a mixture of nudes and textiles which tens to be mostly textile near the village becoming more naturist as you venture further north.
This would, of course, involve flying and renting an apartment or using a hotel, but there is now a substantial Italian influx into the village which might suit your wife.
There are two Italian restaurants on the outskirts of the village, one of which is run entirely by Italians.

As much as I would probably like to go to Fuerteventura for it's freedom I doubt it would be shared.
Actually I've to compose with me willing to enjoy naturism/beach and my wife willing to visit places/museums and so.... Plus the kids... Guess what it's at the bottom of the list.

I'm not too worried about languages as we both speak French and English so I'm sure we can survive in Spain for a week.

My wife and I stayed at El Templo Del Sol last July and, indeed, we were lucky to meet up with Tony (thanks to Naturist Corner) for a visit to the Ebro Delta, including a nice nude walk along a virtually deserted beach.

El Templo is a beautiful and relaxing place to stay, and is next to an absolutely stunning, large naturist beach (El Torn) that I doubt even the most uptight textile would find intimidating.

The solution to getting a reluctant wife into naturism may not be as difficult as some (including Vince) imagine. My wife was certainly not born to be a naturist, but I get around it by booking accommodation in quality naturist resorts, but making sure the holiday is filled with plenty to suit her, too. El Templo fits this model perfectly, because (as well as being a short drive from the delta) it is close to the charming town of Tarragona, and day trips to Montserrat and Barcelona are also very easy. So she sees taking off her clothes in the company of other naked people as a very small price to pay in return for a nice holiday, among nice people (which naturists usually are).

Re not being able to speak Spanish in Spain: it is not an issue for tourists.

Of course it would be awesome that my wife Enjoy naturism too.
So far I would say that reluctant is weak but my position is to respect everyone's belief whatever the topic, as long as my beliefs are respected too.

So i'm not trying to convert her to naturism, but I try to get her used to be around naked people and to make it a natural thing. But at a 10 to 15 days a year it's a very slow process....
From that point if anything should change I would be happy but I don't have and expectations

As much as I would probably like to go to Fuerteventura for it's freedom I doubt it would be shared.

In spite of the island's nude-friendliness the majority of visitors are actually totally textile.