Ah OK, mostly locals, cosy area, especially the little streets around the fresh food market, located in Plaça del Mercat ('mercat' = Catalan, the local language, for market). Good vermouth in Cal Sopena in Carrer del Clot, 55. And if you have a sweet tooth, a visit to nearby Pastisseria La Palma is probably due.
Some ideas as per your "religious" interest:
- A day in the abbey of Montserrat (seen here half thru the video!), one of the epitomes of religious Catalonia, and listening to the children's choir is a must. Check this older post. Yet I would consider this carefully because visiting Montserrat requires at the very least half a day or more, and you're only staying in the city 3 days.
- Much closer, located in the north of the city, in the neighbourhood of Pedralbes: a visit to the monastery of Pedralbes, an icon on Catalan religious history too. Very easy to reach by bus.
- Santa Maria del Mar, a.k.a. as the Cathedral of the Sea because it was built by the fishermen of the district of La Ribera, where the church is located. The nickname became ever more famous lately due to a bestseller novel.
- The Cathedral of Santa Eulàlia, patroness of Barcelona (known simply as "the Cathedral"), especially the cloister. Unfortunately though, it's often too crowded with visitors to really appreciate how it should have been when in was built.
- Barcelona was an important Jewish centre during the Middle Ages, like Girona -the second capital of Catalonia, at 100km north of Barcelona. Unfortunately, some ill-taken decisions in the late 15th century destroyed the centuries' old coexistence with the Jewish community as well as many of the remains of this culture in our land here in Catalonia. Having said that, there are interesting remains left scattered across, and also in Barcelona, like a tiny part of the synagogue located in El Call ("call" meaning "Jewish neighbourhood" in Catalan). For a much better preserved "call", Girona is the place to go.
- Then, of course, there are literally dozens of small churches tucked away in unsuspected places that are a delight to visit, like Sant Pau del Camp or Santa Maria del Pí among others.
... you already mentioned Sagrada Família, so I shall not mention more.
Also to add that in September there's an event called "The night of the Religions" in which 24 of the religious communities in the city from several faiths (Christian, Muslim, Jews, Sikhs...) celebrate an open day (well, night!) in their temples with activities geared towards making their rites and faith closer to the general population. This follows a very successful initiative originated in Berlin in 2012 which aims to break religious prejudices.