Capel-y-ffin is a hamlet near the English-Welsh border, a couple of miles north of Llanthony in Powys, Wales. It lies within the Black Mountains and within the Brecon Beacons National Park. The nearest town is Hay-on-Wye, some 8 miles (13 km) to the northwest.

The Black Mountains are a group of hills spread across parts of Powys and Monmouthshire in southeast Wales, and extending across the England–Wales border into Herefordshire. They are the easternmost of the four ranges of hills that comprise the Brecon Beacons National Park, and are frequently confused with the westernmost, which is known as the Black Mountain. The Black Mountains may be roughly defined as those hills contained within a triangle defined by the towns of Abergavenny in the southeast, Hay-on-Wye in the north and the village of Llangors in the west. Other gateway towns to the Black Mountains include Talgarth and Crickhowell. The range of hills is well known to walkers and ramblers for the ease of access and views from the many ridge trails, such as that on the Black Hill in Herefordshire, at the eastern edge of the massif. The range includes the highest public road in Wales at Gospel Pass, and the highest point in southern England at Black Mountain.