The lost caves of the Amazon
19 June 2012 Last updated at 09:56 BST
Beneath the Amazon rainforest, scientists have recently discovered hundreds of massive caverns in the rich deposits of iron ore.
Most have not been properly explored and researchers believe they may host unique geology and life.
Excavations in one cave revealed evidence of human settlement 9,000 years ago.
Our science editor David Shukman and cameraman Tony Fallshaw were among the first news teams to venture inside.