These awe-inspiring images are some of the first ever taken in a recently-discovered cave so big it has its own weather system.
Cavers are still exploring the recently-found network of vast caverns in Chongquing province, China.
Explorers have discovered that the caves are so large that thick cloud and fog hangs in the upper parts of the underground natural wonder.
Photographer and caver Robbie Shone, from Manchester, was part of a team of 15 explorers on a month-long expedition who stumbled across the cave system earlier this year.
He said: 'It is always very special, knowing that you are the first to step foot into a cave or somewhere where nobody had previously seen, not knowing what you might find and discover.
'Where else on Earth can still hold secrets and mysteries of discovery? That's what I love so much about exploring.
'All the major passageways were deep underground and had never seen light before.
'A few of the caves had previously been used by nitrate miners, at the areas close to the entrance, but had never been properly explored before.'
Rob explained that near-impassable caves like the Tongzi master cave system are only accessible by a long swim or abseiling trip deep into the bowels of the network.
He added: 'We had to be aware of high water levels inside the caves, especially when it rained heavily on the surface. The drainage catchment to these caves is massive and soon the caves can be extremely dangerous and impassable.'