The inner city beaches at Barceloneta and La Vila Olimpica are crowded in the summer months. Easy to get to, you can enjoy the sun and the atmosphere. Those looking for real sand or clean water may be disappointed however.
Heading north on the Blanes train line there are kilometres of beaches including Badalona, Montgat, Masnou, Premia de Mar and so on. Montgat and Masnou are just 20-30 minutes from the centre of the city.

Warning: When it rains beaches near the city may be polluted for a day or two.