The River Wye rises in mid-Wales and joins the Severn at its mouth near the Bristol Channel. For stretches it forms the border between England and Wales; elsewhere it's entirely in Welsh territory. The whole river is beautiful, but "the Wye Valley" usually means the lower section — the dramatic gorge around Symonds Yat and, further downstream, the hauntingly photogenic ruins of Tintern Abbey.
Upstream, the river connects two very different market towns. Hay-on-Wye, just inside Powys, is one of Britain's best destinations for second-hand books. Ross-on-Wye, across the border in Herefordshire, is a quieter place with good walking access to the valley below.
