Sixty percent of Costa Rica's rainforest fauna operates exclusively after sunset. The Pacific coastal lowlands around Manuel Antonio shelter Central America's highest density of two-toed sloths, which descend from canopy refuges at dusk to feed on Cecropia leaves within arm's reach of forest trails. Red-eyed tree frogs emerge from bromeliads. Kinkajous patrol fruiting fig branches. The rustle that sounds like wind is often a troop of white-faced capuchins settling into their night roosts. Manuel Antonio's private reserves open their trail networks to guided nocturnal walks between 17:30 and 20:30, when diurnal species retreat and a different ecological shift begins. These are not national park extensions—they are independently conserved parcels of primary and secondary forest where resident naturalists have mapped every boa constrictor den, every glass frog breeding pool, every strangler fig that cradles a sleeping porcupine. The biological advantage of darkness is visibility. Without the sun's dappled interference, headlamp beams catch the retinal glow of ocelots, the silk threads of wandering spiders, the bioluminescent fungi colonizing decomposing logs. Costa Rica's night forests reveal what day hides. The terrain is the same corridor that connects Manuel Antonio National Park to the Fila Chonta foothills—a biological highway for jaguar, tapir, and peccary migration. Tour operators lease access from landowners committed to maintaining forest continuity rather than fragmenting plots for development. Walk routes rarely exceed two kilometers, but elevation shifts bring microclimatic zones: lowland palms give way to epiphyte-laden oak, where resplendent moth species outnumber those catalogued in temperate Europe. Trails cross streams where spectacled caimans wait motionless in shallows, their eyes two amber points in the beam's sweep. Guides carry red-filter lights to minimize retinal disruption for nocturnal mammals and thermal scopes to locate three-toed sloths concealed in kapok crowns thirty meters overhead. The standard walk duration is three hours—enough time to witness the transition from civil twilight, when howler monkeys issue their final territorial calls, to full dark, when the forest's acoustic landscape belongs entirely to insects, amphibians, and the occasional screech owl.