Two-toed sloths descend after sunset. Bradypus variegatus, the brown-throated sloth native to Costa Rica's lowland and montane forests, shifts from diurnal lethargy to controlled nocturnal feeding, moving branch-to-branch at a metabolic pace one-tenth that of a similar-sized mammal. La Fortuna's proximity to Arenal Volcano National Park and the Bogarin Trail corridor creates a 450-meter elevation zone where secondary rainforest regeneration—following the 1968 eruption—has produced dense Cecropia stands, the sloth's preferred canopy. Nocturnal wildlife walks in La Fortuna target this narrow window. Guides trained in low-light tracking scan emergent branches for the slow silhouette of limbs, the faint gleam of tapetum lucidum—the reflective layer behind a sloth's retina—caught in LED beams. The Bogarin Trail, a private reserve 450 meters west of central La Fortuna, opens its 2.5-kilometer network to self-guided visitors from 07:00 to 17:00 daily, but the $20 entrance fee grants access only during daylight hours. Guided la fortuna sloth night tour tours depart after dusk, when red-eyed tree frogs vocalize and kinkajous emerge from hollow trunks. The rainforest here is transitional—not primary cloud forest, not dry lowland—but a mosaic of second-growth fig, balsa, and guarumo that matured rapidly in volcanic ash. Sloth density peaks where canopy connectivity allows arboreal movement without ground descent, a rare vulnerability for an animal whose muscles generate too little heat for sustained terrestrial locomotion. Naturalist-led walks pair sloth observation with broader herpetological and entomological inventories: glass frogs adhered to underleaf surfaces, tailless whip scorpions on decaying bark, occasionally a fer-de-lance coiled in leaf litter. Night wildlife excursions in the Arenal region have formalized since 2010, when private landowners adjacent to the national park began managing trails specifically for after-dark ecotourism. The model balances low-impact visitation—groups capped at ten, no white-light torches, single-file movement—with economic return that funds habitat corridors. Sloth watching here is not guaranteed; it is probabilistic, dependent on weather, canopy moisture, and the animal's own three-day digestive cycle that governs its descent frequency.