My perfect day would be a spring day, between late May and early June. But we are in February, and Barcelona is also beautiful in winter.
Your only objective for a day of leisure in Barcelona is to abandon yourself to the pleasures that the city has to offer.
First, as a good foodie, I need to think about where to get the best breakfast. A relaxed place where I can read the newspaper and eat the best croissant in town. Hofmann La Seca (Carrer dels Flassaders, 40) in the Born district is definitely my choice. In addition to a latte I order a croissant filled with raspberry or maybe mascarpone, it is difficult to choose, I will order both. Reading newspapers or a good book while time goes by without being noticed is a basic principle of pleasure.