La Rambla street, a chaotic but amazing shopping stretch from the waterfront to Placa Catalunya, is a tourist hub in Barcelona. The 19th Century buildings along both the sides, with lots of restaurants, historic buildings, and souvenir stalls make it really busy. If you are in La Rambla, visit the local market La Boqueria, which is situated in the centre of the street. In the evening, you can find plenty of food options and can try the local drink sangria.
Pro tip: Try avoiding a big meal on this street, as the restaurants are quite expensive. You can just grab a drink and stroll around on the street.