Running in a horse-shoe shape, it passes small market towns such as Llanidloes and quiet villages including Abbeycwmhir and Llanfyllin, traversing central Mid Wales to Machynlleth near the Dyfi estuary and back again across Wales via Lake Vyrnwy and the valley of the River Vyrnwy to Welshpool, close to the English border.
The Hafren Forest lies North-West of Llanidloes, an ancient market town situated in Mid-Wales.
The company was formed in 1859 and parliamentary approval was received on 1 August for the northern section of the line from Llanidloes, Montgomeryshire to Llandovery, Carmarthenshire.
Surveillance of Kemp noted his regular 50-mile commutes between his home in Tregaron and Plas Llysin, an old mansion owned by an American friend Paul Joseph Arnaboldi, in Carno near Llanidloes.
Roland Moyle was educated in Bexleyheath and Llanidloes, and at the University College of Wales, Aberystwyth and Trinity Hall, Cambridge, where he chaired the Labour Club in 1953.