Sites in Merthyr Tydfil

The county borough of Merthyr Tydfil, originally part of Glamorgan, extends for 13 miles north to south, centred on the Taff River and its two upper tributaries (Taf Fechan, Taf Fawr), and 5 miles west to east. The county is bordered by Powys to the north, Rhondda Cynon Taf to the west and Caerphilly to the east. Contained within is a small section of Brecon Beacons National Park, between Llwyn-on Reservoir and Pontsticill Reservoir, including the hills north of the village of Trefechan. The city of Merthyr Tydfil is situated near the river confluence, south of which the county extends for several miles along the Taff valley, incorporating the high ridges on either side, as far as Abercynon. To the north, the Taf Fechan flows through a pretty, tree-lined gorge, containing cascades and narrow sections.

The hills and valleys in the county have a long history of industrial use, and the county contains several disused railway lines, including tunnels and viaducts, plus old coal mines, limestone quarries, factories and iron works. There are two castles in Merthyr Tydfil: Cyfarthfa Castle, a fortified mansion built in the 1820s, and the overgrown, fragmentary remains of the late 13th century Morlais Castle, on a hill above the Taf Fechan.