national park in southern Wales, occupying 519 square miles (1,344 square km) of mountains, moors, forests, pastureland, lakes, and the broad Usk valley. The easternmost highlands in the park are the Black Mountains (old red sandstone) of Powys county, lying east of the River Usk between Abergavenny and Hay-on-Wye, with their highest point at Waun Fach, elevation 2,660 feet (811 metres). Centrally located within the park, south of Brecon, are the Brecon Beacons (old red sandstone), including Pen y Fan, the highest peak in the park, with an elevation of 2,906 feet (886 metres). To the west lies the Black Mountain (chiefly millstone grit) of Carmarthenshire county, east of Llandeilo and south of Llandovery. The park offers a considerable variety of scenery and recreational opportunities, including hill walking, caving, pony trekking, sailing, and angling.