If I had to choose one singular and authentic bar in Barcelona, I'll say "Mendizábal".
This is not a fancy bar, and that's what I love of Mendizábal. But it doesn't mean it isn't a cute one with a beautiful decoration and good prices.
They have a two very differentiated spaces: one privileged terrace in the city center, and the interior salon. Them both are awesome, and it's perfect because you can decide which one fits better with the situation.
They do tapas, sandwich, juices, burgers and veggi burgers.
In my opinion, they have the best vegetarian sandwich offer in town.
But the most important, you can leave the bar without eating their "patatas bravas"
It is a charming and welcome green space in the heart of Barcelona. It has water displays including a beautiful fountain and small lake along with lots of grass verges to lie down and soak up the warm sunshine. A great spot for relaxation, a walk... the place that I like the most is a glass building full of plants inside.
Picnic is a restaurant located in the Born neighborhood. A welcoming environment, pampering every detail. The best brunch in Barcelona. A great team of different countries and knowledge of the world of food and wine. They change the menu every season, looking for fresh products to make family recipes and creative dishes from different parts of the world.