The Ribeira valley, in the south of Sao Paulo state, holds the largest remaining stretch of Atlantic Forest in Brazil, and under it lies one of the great cave regions of the Americas. The park called PETAR, the Alto Ribeira Touristic State Park, covers hills of limestone that are riddled with hundreds of caves, many of them with underground rivers, huge chambers and elaborate formations of stalactites and stalagmites. The forest above is thick with ferns, bromeliads and trees draped in moss, and it belongs to the Atlantic Forest South-East Reserves, a UNESCO World Heritage listing from 1999.
The caves are the main attraction, and several can be visited by anyone with a guide. Casa de Pedra, the House of Stone, has one of the largest cave entrances in the world, a huge arch of rock some two hundred metres high, and Santana cave is known for its beautiful formations. Others have waterfalls, subterranean streams and colonies of bats. Guides are required, and the rules about helmets, lamps and group sizes are strictly applied, so arrange a visit through the park's offices or a local operator. The forest above has jaguars and tapirs, though sightings are extremely rare, and many kinds of birds.
The roads of this region are fine riding, though it is one of the poorer parts of the state, with small villages and long stretches of forest. The highway from Apiai towards Iporanga winds through hills with bends, steep sections and some patched surfaces, and in the wet season, from December to March, heavy rain can cause landslides and make unpaved side roads slippery. The dry months, from April to September, are cooler and safer. Mist often lies in the valleys in the morning, and the air is rich with the smell of damp earth and leaves.
Apiai, seventeen kilometres away, has fuel, shops and restaurants, and is the best base. Villages inside the park area have small guesthouses and simple food, with rice, beans, manioc and river fish. Carry water, insect repellent and a light waterproof, and wear sturdy shoes for the cave floors, which can be wet and slippery. The local people are welcoming and used to travellers.