I am not a great fan of the dog parks in Barcelona.
I have two main reason for this.
One is that some owners are not responsible and do not clean up after their dogs. This leads ot worm and parasite infestations, as well as infectious diseases like kennel cough being easily transmitted.
The second is that dogs in dog parks can be misunderstood. Very often what is observed as "play" is a dog or group of dogs finding out exactly who is Top Dog and where they stand in that park's constantly changing and dynamic hierarchy. Dogs will always sniff each other to first gather this information. Once they have gleaned everything possible from this doggie "greeting" they then choose their next action. They may ignore the other dog and walk away or they may progress to other dominance behaviour such as mounting, jumping onto the neck of another dog, standing over them, holding a trophy (such as a ball) and postering with it etc. Many dogs act out these behaviours good naturedly, but other dogs are aggressive with their behaviour and yet others are timid and would much rather be sitting near their owner on a beach or lying on the couch. Whether the dog is the most dominant or the least dominant, dog parks can be stressful for all of them as they try to maintain their status or protect themselves or their owners.
When your dog meets another dog where the above behaviours are acted out equally on both sides and they both rest in between bouts of play, you will know that your dog has found a true mate. It is then worth introducing yourself to the owner and arranging a time when the dogs can interact again.
From my experience the things to look out for if you are visiting a dog park are:
Here is a link for dog parks in Barcelona. Enjoy and be responsible.