Based on the Manialtepec lagoon itself, sixteen kilometres west of Puerto Escondido, rather than selling the trip from a desk in town.
Their long evening runs thirteen kilometres through the mangroves at dusk, a fire on the empty Playa Puerto Suelo, and then a night swim in the bioluminescence — dinoflagellates that flare blue-green wherever the water is disturbed, so that every stroke leaves a trail. It works best on a moonless night and in the warm months; a full moon washes it out completely, and any operator who tells you otherwise has not checked the calendar.
The lagoon is also one of the better birding sites on this coast, with several hundred species recorded.