Barcelona, Ascension May 14

Catalans -citizens of Catalonia, where Barcelona is capital from- are not very religious these days, generally speaking that is. Despite the old stereotype dragged on by many foreign books about "being a Catholic country", the reality is that albeit a sizable chunk (especially the older generations) are believers, only a small portion of the population are actual church-goers. When it comes to religious celebrations/rituals, there's a lot of "... it has always been like this" rather than religious fervour in itself. Thus, you'll see still quite a few religious weddings or crowds participating in the Easter parades for example, but for the rest of the religious holidays most people takes it as an off-day rather than anything else. Not to ignore of course, there is a small portion of the population (all ages) who're devoted Catholics, but it's a minority.

But... May 14th is not an official holiday in Catalonia, it's a working day.

What Enric said. Barcelona is the least religious city in the least religious region of Spain. There will probably be extra masses at the Cathedrals. Other than that you probably won't notice that it's a religious holiday at all.