A swath of wide sandy beaches stretches from La Serena's nonfunctional lighthouse right to Coquimbo: there are so many that you could visit a different beach every day for a two-week vacation. Unfortunately, strong rip currents make some unsuitable for swimming – but good for surfing. Safe swimming beaches generally start south of Cuatro Esquinas.
Those between the west end of Av Francisco de Aguirre and Cuatro Esquinas (ie closer to town) are friskier and generally dangerous for bathers. Look for the signs 'Playa Apta' (meaning beach safe for swimming) and 'Playa No Apta' (meaning beach not safe for swimming).
For quick beach access, take either bus Liserco or colectivos running between La Serena and Coquimbo, and get off at Peñuelas and Cuatro Esquinas, a block from the beach. During January and February direct buses (CH$500) head down Av Francisco de Aguirre to Playa El Faro. During the remainder of the year, you'll have to take a colectivo (CH$600) or do the 3km walk to the lighthouse from town.