Laguna de Manialtepec is a brackish coastal lagoon about twenty minutes west of Puerto Escondido along Highway 200. By day it is a bird-watching destination of note, with mangrove channels harbouring herons, kingfishers, ospreys, roseate spoonbills, and occasionally crocodiles. Boat tours from Puerto Escondido take you through the mangrove tunnels and out onto the open water.
By night — specifically on moonless nights — the lagoon transforms. Every movement in the water produces a streak of cold blue-green bioluminescent light. Swimming through it, or simply dragging your fingers overboard from a kayak, is one of the more extraordinary natural experiences on the Mexican coast. Tour operators in Puerto Escondido run evening boat trips and kayaking tours to the lagoon; choose carefully, as boat numbers are regulated and some operators are more responsible than others.