Lerici's own beach is a small crescent of sand and pebble in front of the harbour — pleasant enough but not exceptional, and busy in summer. The better swimming is slightly outside town.
San Terenzo, a 2 km walk north along the promenade, has a wider beach with calmer water and a more local clientele. Fiascherino, south of Lerici on the road toward Tellaro, is a small cove popular with families, with clear water and some shade from pines at the back of the beach. Both are reachable by boat from Lerici harbour or on foot in under an hour.
For serious beach days without the crowds, take a boat to the beaches below Portovenere or to the small island of Palmaria just across the channel — the rocks there are excellent for snorkelling.