Despite remaining largely off limits for most of this century, Ilha Grande’s recent tourism explosion means that preservation and sustainability have become more important than ever.

The coastline south of Rio de Janeiro is not called the Costa Verde (Green Coast) for nothing. Lush, jungle-clad mountains descend precipitously to the sea, with sparkling beaches, hidden coves and picturesque harbours hugging the shoreline. Even more impressive are the scores of islands scattered offshore, and the most dramatic of all is the appropriately named Ilha Grande (Big Island), a mountainous island roughly three times the size of Manhattan.

Home to some of Brazil's most enchanting scenery, Ilha Grande has more than 100 white sand beaches and its hilly interior is densely covered with a pristine swath of Mata Atlântica, the biologically-rich Atlantic rainforest that has largely disappeared from other parts of the Brazilian coast. Waterfalls, craggy peaks and topaz lagoons are all part of the scenery, while abundant wildlife flourishes. Howler monkeys, marmosets and red-browed Amazon parrots are among the more commonly-spotted species.

Yet despite its obvious allure, Ilha Grande has remained largely off limits for most of this century. In the 1930s, the fascist-leaning government of Getúlio Vargas built a penal colony on the island to house political prisoners. In later years, hardened criminals were thrown into the mix, and by the 1960s the Cândido Mendes penitentiary had become one of Brazil's most notorious criminal breeding grounds (indeed the formidable drug gang Comando Vermelho was born here in 1979). Escapes were not uncommon, including a brazen helicopter getaway in 1985 by José Carlos dos Reis Encina, who was known as “Escadinha” (Stepladder) for his innovative flight.

With operating costs rising, the prison was permanently closed in 1994, and the island's tourism potential at last arrived. Less then a decade ago, accommodation on the island was limited to a handful of simple pousadas (guesthouses). However, the island’s growing popularity with both Brazilian and foreign travellers and its relatively convenient access to Rio (a 2.5-hour bus ride, followed by an 80-minute ferry journey) soon attracted ever-larger crowds, and tourism has exploded over the last five years. Today there are more than 100 lodging options on the island, most of which are located in the main settlement of Vila do Abraão.

A 2009 decree signed by Rio state governor Sergio Cabral relaxed the 23-year-old environmental protections that limited development on Ilha Grande and 93 other islands in the state. Local organisations like CODIG (Committee for the Protection of Ilha Grande) are lobbying to repeal the decree, but for now, preservation and sustainability have become the buzzwords of the day on the island. Much of its land remains protected by the federal and state laws, which prohibit picking plants, feeding animals, open fires and bush camping. Some areas -- like the Reserva Biológica Estadual da Praia do Sul, a 3,600-hectare protected biological reserve that protects five different ecosystems -- rainforest, dunes, mangroves, lagoons and rocky coastline -- are entirely off limits to all but research scientists.

Vila Abraão, however, continues to grow, with the opening of more guesthouses, restaurants and bars. During summer weekends and on holidays (particularly over New Year's Eve in January and Carnaval in February or early March) a mix of Brazilian and Argentine sunseekers -- and a handful of international visitors -- pack the sandy streets, overwhelming the calm that pervades the island for the rest of the year. Some of the 6,000 residents even complain that things were better in the prison days when people were forced to come and everyone wanted to leave.

For the moment, however, the island remains free of high-impact resorts, and the majority of the guesthouses are taking a small-scale approach with a focus on ecotourism. Retreats like The Island Experience allow visitors to experience Ilha Grande's splendour through a program of sea-kayaking and hiking, along with yoga and capoeira (Brazilian martial art) workshops from its ocean-front perch. Pousada Naturalia, seamlessly built in the rocky hillside overlooking Vila do Abraão beach, has handsomely designed all-wood rooms, seafront balconies and solar-heated showers. A little further east, Asalem has gorgeous views over the rainforest and bay, with kayaks and canoes available for exploring the shoreline, and is run by acclaimed photographer André Cypriano, who produced an eye-opening book of photos documenting life inside Cândido Mendes before its closure. A new crop of eco-minded guesthouses, like the Australian-run Pousada Aratinga, are even promoting waste reduction, recycling and composting.

Development completely disappears once you stroll beyond the boundaries of Abraão -- and stroll you must as no private cars are allowed on the island and the limited public transport is for island residents only. Dirt paths skirt through rainforest and along the shoreline, leading to Ilha Grande's postcard-perfect beaches, past colonial ruins and up to the steep mountain slope of 982m-high Pico do Papagaio, which affords 360-degree views over the island.

One of the best activities is to explore the island’sintriguing past. A 7km hike from Vila do Abraãoto to the south side of the island leads to the ruins of the Cândido Mendes penitentiary and the ghostly settlement of Dois Rios, a handful of dwellings where the prison guards formerly resided and where trees now grow through the middle of abandoned houses. The path leading 6km east from Abraão winds through jungle, past tiny inlets and bays before reaching the stunning beauty of Praia do Lopes Mendes, whose dazzling white sands consistently earn it a ranking among Brazil's top 10 beaches. A shorter jaunt is the 1.7km Circuito do Abraão, which leads from Vila do Abraão to the moss-covered ruins of Ilha Grande's first prison, Lazareto, passing a 19th-century aqueduct next to a picturesque swimming hole where local  children splash about on their way home from school. Beyond the aqueduct , a trail leads to Cachoeira da Feiticeira, a refreshing 15m waterfall, before continuing to the beach of Saco do Ceu, whose calm lake-like waters make a marvellous setting for a swim.

While there are plenty of memorable walks on the island, you can also sign up for an outing with the sustainably-minded O Verde. Run by Argentine expat Gigi Courau, O Verde offers guided hikes, kayaking and snorkelling trips and visits to local island communities. For trips to beaches further away, book a boat trip with one of a handful of operators based at Abraão, such as Sudoeste SW. You can also negotiate a pick-up and drop-off with one of the local fishermen, who know some of the most idyllic spots. And if you would like to explore the riches beneath the sea, sign up for a dive with Elite Dive Center to see the abundant marine life and a number of shipwrecks -- some of which date back to the 16th Century.

There is much to explore on the island, and it is still easy to find a quiet stretch of shoreline backed by virgin rainforest and relax for a spell. In the future however, this slice of paradise may not be so easy to come by.