Gruta do Janelão: Brazil's Skylight Cave in the Peruaçu Canyon
In the dry, karst-riddled hills of northern Minas Gerais, a cave river cuts through a mountain and pours daylight straight into the earth. Gruta do Janelão, inside Peruaçu Caves National Park near the town of Januária, is one of Brazil's largest and most celebrated caverns, known not for a single grand chamber but for a chain of collapsed skylights that let sunshine and living forest reach far underground. Carved by the Peruaçu River as it worked through limestone over a very long span of geological time, the cave stretches for several kilometres beneath the hills, its floor dropping well over a hundred metres from entrance to interior. Wherever the ceiling has given way, beams of light and rain reach the passage floor, and something unexpected happens: trees grow inside the mountain.
A river that carved a mountain
The story of Gruta do Janelão begins with water and rock. The Peruaçu River is one of the few permanent tributaries of the mighty São Francisco River, and for millions of years its slightly acidic waters have dissolved their way through a thick limestone massif belonging to the Bambuí Group, a sedimentary formation that underlies much of this part of Minas Gerais. Rather than staying on the surface, long stretches of the Peruaçu disappear underground, following joints and bedding planes in the rock until they widen into tunnels and, eventually, into galleries large enough to be called caves in their own right. Janelão is the grandest expression of this process in the whole valley: a single continuous passage carved by flowing water, long enough and tall enough that it functions less like a cave and more like an underground canyon.
Windows in the roof
The cave takes its name from exactly the feature that makes it famous. "Janelão" means something like "big window" in Portuguese, a reference to the openings, known locally as clarabóias, where sections of the cave roof have collapsed over time. These are not small cracks but substantial breaches, wide enough to flood entire stretches of passage with daylight. One of the best known is shaped distinctly like a heart and is referred to as the Clarabóia do Coração, the Heart Skylight. Rather than a single opening, Janelão has a whole sequence of these skylights spaced along its length, so that a visitor moving through the cave alternates repeatedly between deep cave darkness and bright, plant-filled clearings lit from directly above.
Forests inside a cave
Where sunlight reaches the cave floor through these openings, a genuinely strange habitat takes shape. Seeds arrive on the wind or are carried in by animals and birds, rain falls freely through the gaps, and small stands of trees, shrubs and ferns take root on the cave floor, right beside the underground course of the Peruaçu River. Visitors and researchers have long compared the effect to carefully tended Japanese gardens, with their sense of delicate order set against the raw, dark limestone walls around them. It is one of the more vivid demonstrations in the caving world of how light, rather than its absence, can define a cave environment, turning sections of Janelão into isolated pockets of forest that exist nowhere else on the surface in quite the same form, sheltered on every side by rock.
Giants of stone and collapsed ground
Janelão's scale shows up in its individual features as well as its overall length. The cave holds one of the longest stalactites ever documented, reportedly reaching around 28 metres, an extraordinary formation built up drip by drip over an immense stretch of time. Above ground, two of the collapse structures associated with the cave are large enough to be classified as tiankengs, a term used for giant sinkholes whose diameter and depth both exceed 100 metres. One of these, known as the South Doline, is not directly connected to the main passage of Janelão; cavers believe it once linked to the cave as a tributary channel before debris sealed the connection, leaving it as a separate, dramatic void in the landscape above.
Life in the dark zones
Away from the sunlit clearings beneath the skylights, Janelão still behaves like an ordinary cave, and it supports the fauna typical of Brazilian limestone caverns. Bats roost in its darker reaches, and biologists surveying caves across this part of Minas Gerais have documented troglobitic species, animals so specialised to permanent darkness that they exist nowhere on the surface, including whip spiders and harvestmen adapted to a life without light. These creatures occupy the opposite end of the same passage that, just metres away, opens onto a sunlit stand of trees, underlining how unusual Janelão is in containing both extremes within one continuous cave system.
A hidden corner of Minas Gerais
Gruta do Janelão sits within Peruaçu Caves National Park, a protected area established in 1999 in the far north of Minas Gerais state, spanning the municipalities of Januária, Itacarambi and São João das Missões. The park covers tens of thousands of hectares of rugged, sparsely populated terrain where the vegetation shifts between two of Brazil's great biomes: the wooded savanna of the Cerrado and the thornier, more arid Caatinga. This transitional setting, combined with the underlying limestone, has produced an unusually rich concentration of caves, with well over a hundred caverns catalogued inside the park boundaries, of which Janelão is simply the largest and most dramatic. The climate here is markedly seasonal, and the Peruaçu River itself swells and recedes through the year, which in turn affects how much of the underground passage is walkable and how the light-filled clearings look from one season to the next.
Traces of ancient lives
Long before the region became a national park, people sheltered in these caves. Archaeologists working in the Peruaçu valley have documented rock paintings more than 10,000 years old on the walls of Janelão and several neighbouring caves, alongside human remains recovered from rock-shelters such as Lapa do Boquete and dated to roughly 7,000 years ago. Left by populations who lived along the river and used the caves for shelter, ceremony or burial, these traces make the park one of the most significant records of early human presence in this part of South America, layered directly on top of a landscape shaped entirely by water and stone.
A landscape recognized by the world
That combination of geology, ecology and human history was formally recognized in July 2025, when the Peruaçu River Canyon was inscribed on the UNESCO World Heritage List as a natural property. The listing specifically highlighted the rare pairing found here: a dramatic karst landscape and monumental cave galleries like Janelão sitting alongside ancient rock art and long-term archaeological evidence of human occupation. For a region that receives relatively few visitors compared with Brazil's coastal attractions, the recognition places Peruaçu firmly among the country's most important natural and cultural sites. Access to Janelão itself remains carefully managed, with visits generally requiring an authorised guide, both for visitor safety on the uneven, water-carved floor and to protect the fragile forest patches and archaeological traces found throughout the passage.
Explore on the map
Gruta do Janelão sits at the meeting point of deep time, flowing water and human history, all inside a single cave passage lit by its own collapsed roof. To see exactly where it lies within Peruaçu Caves National Park, and to browse other caves and karst landscapes documented around the world, open the interactive map and search the region around Januária, Minas Gerais.