A true wonder of geography, Dashiwei Tiankeng is the largest of its kind in the world and yet has only been known to the outside world since 1998. Tiankeng, literally "sky pit" in Chinese, refers to the large vertical-sided collapsed caves that have formed over millions of years. This is a giant of a tiankeng, 600m (1,968 ft.) from east to west and is 613m (2,011 ft.) deep with unbroken, vertical perimeter walls that cut through three conical hills. The virgin forest at the bottom covers an area of 96,000 sq. m (1,033,335 sq. ft.) and is home to rare species such as the flying squirrel. A long section of downstream river cave lies below the edge of the breakdown pile on the tiankeng floor. The park is home to a suite of large tiankeng and major cave systems that are only partly explored. The tour bus gives glimpses of rims and walls of the various tiankeng, with roadside stops above the degraded Datuo Tiankeng and another at the lip of Maoqi Dong. The bus then drops visitors off to walk around the rim of Dashiwei Tiankeng. The ticket office is refreshingly honest here, warning visitors when cloud conditions make viewing impossible. In fact, I spoke to one couple who had been here four times and had never yet seen the interior of Dashiwei. The paths are lined with blackberries while the sound of cuckoos and cowbells echo away into the distance.