A huge ancient forest world has been discovered 630 feet underground, down a sinkhole in China.

The underground mystery was stumbled upon in a Chinese 'Geopark' by a cave exploration team of scientists, in May last year.

The phenomenon is also known in China as 'tiankeng' or 'heavenly pits'.

Leye Fengshan UNESCO Global Geopark, where the sinkhole was found, is located in Guangxi Zhuang Autonomous Region, Southwestern China.

The Geopark is described on the UNESCO website as 'primarily sedimentary with more than 60% of 3000m thick Devonian to Permian carbonate rocks.'

It's known for being 'the territory of caves and of the world's longest natural bridge'