If you want to escape the crowds and enjoy a nice golden sand and some beach games, head here. The beach is mostly visited by locals, so it doesn't get very crowded. The beach has all the usual amenities - a lifeguard, showers, toilets, and disabled access. There are also some beach bars and restaurants.
Wikipedia https://fr.wikipedia.org/wiki/Plage_de_la_Nova_Mar_Bella
More information https://meet.barcelona.cat/en/discover-barcelona/districts/sant-marti/nova-mar-bella-beach
Address (Unnamed Road), 08019, Spain
Coordinates 41°24'7.077" N 2°12'55.259" E