The round tower stands on the valley floor, not on a hill where you would expect a castle to be. It went up around 1230 inside an older stone bailey, replacing a shell keep from the mid-12th century that had itself replaced Picard's earthwork motte from the end of the 11th. The castle's last documented emergency garrison was in 1403, when Owain Glyndŵr's rebellion made a cylinder of stone in the Rhiangoll valley worth defending again.
A short walk away, across the castle green, stands Tretower Court, one of the finest medieval houses in Wales, built by Sir Roger Vaughan and his descendants across the 15th century: the west range after about 1447, the north range after 1460, and an embattled gatehouse added by Sir Thomas Vaughan around 1480.
Sir Roger was captured by Jasper Tudor during the Wars of the Roses and executed. The family left shortly after 1700, and the abandoned house declined under tenant farmers until its former noble rooms were being used to keep pigs. It was bought for the nation in 1934 and restored over the decades that followed.
Inside, the rooms are furnished with replicas based on 15th-century evidence. There is a green-earth painted cupboard carrying the Vaughan emblem, a boy with a snake around his neck, and a painted cloth that runs from Agincourt to the siege of Harlech. Cadw calls the whole thing "one of the finest medieval houses in Wales."
The visitor centre has a gift shop, toilets, baby changing and parking, an audio tour and a recreated medieval garden. Dogs on short leads are allowed at ground level. The café, Y Bwyty Bach, is closed until further notice, so bring what you need or plan to eat elsewhere.
For eating elsewhere, the Nantyffin Cider Mill Inn sits a little out of the village at the junction of the A40 and A479, run by Chris and Penny Skinner. It began as a 16th-century drovers' inn and made cider in the 19th century; the name means the brook by the border. The pub's diners single out the fish and chips, a beef Sunday roast and a vegetarian nut roast with cauliflower cheese, and there is one changing cask beer, usually from a Welsh brewery, alongside real cider. There is a garden, a separate bar and a children's play park.
The Church of St John the Evangelist is late Victorian, built in 1876-77 by J. L. Pearson in red sandstone with buff-yellow dressings, a double bellcote and trefoiled wind-braces inside. Nothing in it predates the rebuild, though a disused medieval stoup survives outside the nave, the remnant of an earlier church, reputedly dedicated to St Michael, that had fallen into disrepair.
A seven-mile circular from Bwlch passes the court through the Rhiangoll Valley, with views toward Pen y Fan and Llangorse Lake; an eight-mile moorland circuit climbs from the court past a Roman fort to Cefn Moel; and a gentler pilgrimage route from Llangynidr follows the Usk and the canal, calling at St John's before crossing to St Michael's at Cwmdu.
Crickhowell is three miles south-east down the A479, a market town with independent shops, among them Natural Weigh and the Book-ish café and bookshop, a ruined Norman castle, and a bridge that shows twelve arches from one side and thirteen from the other. Abergavenny, eleven miles on, has the nearest railway station. The X43 between Brecon and Abergavenny stops about 400 metres from the court.
John Leland, passing through in the reign of Henry VIII, wrote it down as "a smaulle village stonding on a little brooke." A brook still runs through the village, and south of the court the leat of a probable lost mill survives, one that may have fed the castle moat.