At 4 a.m. the minivan eases out of Cartagena under a sky still thick with humidity; the coast unspools eastward and the road becomes a ribbon through palm and scrub. By midmorning the mountains of the Sierra Nevada taper toward the Caribbean and the entrance gate to Tayrona National Natural Park—one of Colombia’s most fiercely protected coastal reserves—appears like a green slash against blue water. The guide reads a short orientation, and then the trail takes over: two hours of humid forest, roots and boardwalk, gulls calling over reefs until the wide bowl of Cabo San Juan de Guía opens, a sweep of white sand flanked by rocky arms and a narrow cove known as La Piscina.