Michael Portillo is on Northern Ireland's spectacular Causeway Coast to begin a railway journey that takes him along the north and east coasts of Ireland through the provinces of Ulster and Leinster.Beginning on the windswept shores of Loch Foyle, he investigates the 17th-century origins of Ireland's sectarian divide, braves choppy seas to join an archaeological expedition, meets local teenagers learning about their costal home, and surveys the spectacular basalt landscape of the Giant's Causeway.