In the southern portion of China there is an expansive karst landscape, formed by the dissolution of soluble rocks such as limestone, dolomite, and gypsum. The region is home to the South China Karst UNESCO World Heritage Site, which is actually seven different notable features, as well as the visually impressive Moon Hill, some of China's supercaves, and Xiaozhai Tiankeng, the world's deepest sinkhole. You can climb Moon Hill, but it's best to plan ahead. You can also explore China's great caves, but it is necessary to explore between October-November and February-March to avoid the monsoon seasons, and getting down Xiaozhai Tiankeng requires a lot of gear. You can read more about the Tiankengs (giant dolines or sinkholes) in the karst of China (PDF).
Current TV previously & previously, the media company founded by Al Gore after the 2000 election, has picked up the kinds of in depth long form journalism being rapidly dropped by major networks, but has been tantalizingly unavailable for those without cable; until now. They have been putting their Vanguard episodes up on their website and on YouTube. [more inside]