The Heart of Wales Line between Swansea and Shrewsbury is surely one of the great railway journeys of Wales - 120 miles of breathtaking scenery, through picturesque farmland, valleys, towns and villages. Taking 29 years to build between 1839 and 1868, the line is one of the engineering wonders of Wales.

In this week's Jamie's Welsh Journeys (Tuesday, November 22, BBC Two Wales/2W), Jamie takes a train ride from Llandeilo to Knighton on the English border, discovering some of the country's hidden landmarks along the way, from Roman remains to a copper sea monster.

It is difficult to imagine a more peaceful place than Llandeilo. The town's 13th century castle is now a tranquil monument of days gone by. But things weren't always so quiet. "There is evidence that contrary to popular belief, the local Celts put up a very strong fight against the Romans," says Gwilym Hughes, an expert from the Cambria Academy who has been excavating Roman remains at Llandeilo.

The Heart of Wales line was built in the 19th century to connect the industrial towns of northern England to the ports of south Wales, and although it is now more of a tourist route, many of the towns along the line are in many ways unchanged.

The market town of Llandovery is Jamie's next stop. Originally a drover's town, Llandovery is still frequented by farmers who come to sell their cattle. "You could have come here anytime in the last two centuries and it would be the same," says Jamie. "It is timeless."

From Llandovery, Jamie travels east to Llanwrtyd Wells where he encounters a group of face painted Morris Dancers, then it's on to Llandrindod Wells in the heart of mid Wales.

One of the most popular of Welsh spa towns, Llandrindod Wells exudes Victorian gentility. Despite the relaxed atmosphere and opulent architecture there is something else that draws the tourists these days - a huge copper sea monster in the town's lake.

In the most British ritual, Jamie enjoys afternoon tea served by train enthusiasts on Dolau railway station, before jumping back on the railway.

Jamie's last stop is the town of Knighton. Although the town is in Wales, Knighton's railway station is in England so Jamie must cross the border back into Wales. Derek Price MBE, the town crier is waiting to greet him - causing a stir with the locals.