Cacaluta is a 1km-long slice of paradise that's protected by an island, backed by dunes and usually deliciously deserted. The Mexican road-trip movie Y Tú Mamá También was famously filmed there. Swimming is possible, although there can be undertow. Snorkeling is best around the island. There are no services at the beach, so bring plenty of water. Lancha (motorboat) is only way to currently get there.
There is technically a trail to the beach, the Sendero Zanate, but it was closed to the public at last visit.