Graham Hancock travels to the underwater site at Yonaguni in Japan that he has been studying in his hunt for signs of ice age inhabitation. Best-selling, yet controversial author Graham Hancock scours the seas in a bid to find evidence of a lost civilisation in this new series, Underworld. At the end of the last Ice Age, huge areas of land were submerged by rising sea levels - the same areas that are likely to have been inhabited by man. But archaeologists have concentrated their search for past civilisations on land and so date the dawn of civilisation to around 6,000 years ago. Hancock contends that underwater evidence points to a much earlier starting point for organised settlement.