Abercynrig is a well preserved, largely unaltered late seventeenth-century manor house situated on the south side of the Usk valley, a few kilometres east of Brecon.

Abercynrig is a two-storey, four-bay symmetrical house of rendered stone with a steeply pitched, hipped stone roof with swept eaves and dormer windows on the west side. The main entrance is a single-storey projecting porch in the middle of the east side. This is flanked by slightly projecting wings to the north and south. The windows, now sashed, were formerly mullioned and transomed. To the south a single-storey stone extension joins the main building to the Granary, a two-storey stone building with a pitched slate roof, aligned east-west. This has small mullioned windows and modern dormers in the roof.

The earliest house on the site was probably built by the Aubrey family in the thirteenth century. By the fourteenth century the family, first recorded in Brecon, has risen to local prominence and during the sixteenth century Dr William Aubrey (circa 1529-95) rose to national prominence as an intellectual and lawyer. He was MP for Carmarthen in 1554, Brecon in 1558 and his great wealth enabled him greatly to increase his estates. Within the present house there are traces of an earlier, sixteenth-century one that was probably built by Dr Aubrey. The antiquary John Aubrey, in Brief Lives, states that Dr Aubrey, his great grandfather, bought Abercynrig from an Aubrey cousin and that he built the 'great house at Brecknock: his study looks on the river Usk. He could ride nine miles together on his own land in Breconshire'. After his death the family declined rapidly in prosperity, his grandson Sir William Aubrey, of Tredomen, finally squandering the entire fortune. This forced the sale of Abercynrig in 1621 to Jeffrey Jeffreys, a prosperous mercer of Brecon. By 1651 the Jeffreys family had bought all the Abercynrig lands.

The present house was built by a member of the Jeffreys family, probably Colonel John Jeffreys, in the 1680s and apart from the insertion of sash windows in the nineteenth century has been little altered. It retains its seventeenth-century woodwork, fireplaces and staircases, with contemporary painted panels over the main fireplaces depicting the story of Diana and Actaeon. The Granary is probably contemporary, possibly retaining earlier elements. In the wall between the house and the Granary is a Tudor doorway from the earlier house. The joining extension was built in the 1930s and the doorway inserted then.

In the early eighteenth century Abercynrig passed through marriage to an Irishman, Thomas Flower. His descendant, William, 3rd Viscount Ashbrook, sold Abercynrig in 1800 to John Lloyd, of Dinas, Llanwrtyd (died 1818). John Lloyd had made his fortune in the East India Company. He built a new family home, Dinas, Brecon, which was not occupied until 1828, and lived at Old Oak House, Brecon. Dinas became the chief Lloyd seat and Abercynrig was tenanted until 1941, when it was requisitioned and Sir John Conway Lloyd went to live first at The Granary and then in the house itself. During the 1920s and 30s Abercynrig had been lived in by Captain D'Arcy Hall, who converted the Granary into a playroom and built the joining extension, then a servants' hall, now a dining room. The present owner is Sir John Lloyd's only surviving son.