In this episode, Julia faces an epic walk, in more ways than one. Not only is this the longest and arguably most dramatic walk yet, but it passes through the unruly territory of Scottish clans and Rob Roy. The Highlands were a place to be wary of, until the railway arrived.

The backstreets of Weymouth seem an unlikely spot to explore railway history, but Julia discovers there was once a short railway that ran south from Weymouth and across the unique coastal features of Chesil Beach and Portland. The walk is the ideal platform for learning about the history of Portland Harbour and the tied isle's most famous export, Portland stone.

Her first walking foray into Scotland has a very distinct flavour to it: whisky! The Speyside Way is one of Scotland's great walking routes, and between the villages of Craigellachie and Ballindalloch it follows the route of the railway that once served a remote area and a world-famous drinks industry.

Tin and copper once made the area around Redruth the richest patch of land in the country. They inspired great engineering feats and pioneering tramways, the forebears of the rail empire. Julia has her work cut out as she crosses an entire country, winding past Cornwall's crumbling engine houses and following a railway that has not operated for 140 years

Julia walks along the stunning Mawddach estuary in north Wales. The area between Dolgellau and the coastal resort of Barmouth is one of the least visited parts of Snowdonia, but in the 1860s it received a great rush of holidaymakers, taking advantage of the new railway that connected the valley to the cities of England.

Julia begins her exploration of Britain's lost rail empire in Derbyshire, the heart of the Peak District, with a walk along the popular Monsal Trail. Limestone cliffs and gorges abound, not to mention the tunnels and soaring viaducts of the Midland Railway - one of the most dramatic and unlikely main lines ever built.