The park sprawls across 332,000 hectares and 25 municipalities, making it the largest continuous Atlantic Forest reserve in Brazil and a component of the UNESCO World Heritage-listed Atlantic Forest South-East Reserves. Eight visitor centers -- called nuclei -- offer entry points along its length, each with a different character. The Cunha nucleus draws hikers to the Pedra da Macela trail, where the reward is a panoramic lookout over the serra's undulating ridges. The Itutinga-Pilões nucleus, closer to the Baixada Santista lowlands, offers gentler paths through dense forest to the Cascata da Serra do Mar waterfall. Some nuclei keep regular hours; others require advance booking. Either way, a visit here is not a casual park stroll. The terrain is steep, the forest thick, and the trails earned.

The Serra do Mar's escarpment catches moisture-laden air rolling in from the Atlantic, wringing it out as rain that feeds hundreds of streams and waterfalls. At the Cunha nucleus, the Cachoeira do Pocinho offers a swimming hole cool enough to shock after a humid climb. The most rewarding trails lead to ridgetops where the canopy drops away and the coast unfolds below -- the port of Santos, the beaches of the Litoral Norte, container ships tiny as toys on the blue water. On clear days, the view alone justifies the sweat. On foggy ones, the forest itself becomes the attraction: bromeliads clinging to trunks, orchids in the understory, and the constant percussion of dripping water.

This is Atlantic Forest, a biome that once covered 1.3 million square kilometers of Brazil's coast and has been reduced to roughly 12 percent of its original extent. What survives in the Serra do Mar is among the richest remaining fragments. Over 450 species of trees can crowd a single hectare. Some 373 bird species have been recorded within the park, along with 111 mammal species -- nearly half of the Atlantic Forest's total mammalian fauna. Endemism runs remarkably high: more than half the tree species and 92 percent of the amphibians found here exist nowhere else on Earth. Walking these trails, you are moving through a forest that has been evolving in relative isolation for millions of years.

The park is not uninhabited. Traditional communities still live within its boundaries: quilombola settlements, founded by descendants of enslaved Africans who escaped captivity and built lives in the forest's refuge; caiçara fishing communities along the coast, whose culture bridges the marine and terrestrial worlds; and indigenous Amerindian groups who maintain ancestral connections to this land. Their low-impact ways of life have coexisted with the forest for generations. Tour agencies based in nearby cities can arrange guided visits, handling the permits and logistics -- a practical choice for visitors unfamiliar with the park's scattered nuclei and booking requirements.