Michael Portillo steams through the glorious scenery of the Snowdonia National Park on one of Britain's greatest heritage lines, the Welsh Highland Railway. Stopping off at Beddgelert, Michael takes in the awesome geology, which inspired Charles Darwin.Back aboard the Welsh Highland Railway, Michael heads for Caernarfon, in whose 13th-century castle King Charles III was invested as Prince of Wales in 1969. Michael heads for the coast, where the Menai Strait separates mainland Wales from Ynys Môn, or Anglesey, to find the heart of the United Kingdom's mussel industry.Continuing along the Menai Strait, Michael reaches its earliest road crossing, an elegant suspension bridge designed by the Scottish engineer Thomas Telford and opened in 1826. And from Bangor, Michael takes the train across the Britannia Bridge to the first station on Anglesey, known as LlanfairPG, to visit the island's sea zoo.