New Zealand's Northern Explorer, the longest-running passenger service in the country. The train travels 423 miles along the historic North Island Main Trunk Line on a 12-hour voyage and the journey takes travellers through some of the most astonishing landscapes of the southern hemisphere from volcanoes to coast and from lava fields to unspoilt islands. Historians explain the history of the railway and tell the tale of the terrible tragedy at Tangiwai, when over 150 people were killed by a volcanic mudflow that hit the train.