Craig-y-Nos is a large castellated country house set on a terraced bank overlooking the River Tawe. The original house (now the main South block) was designed by TH Wyatt and built in 1842 for Rhys Davies Powell. The North block of the house and other additions including the clock tower, winter garden (now the Patti Pavilion, Swansea) and theatre of 1891, were added by Bucknall and Jennings of Swansea for Adelina Patti, the renowned soprano, who bought Craig-y-Nos in 1886. The castle is a Grade Two Listed Building and the theatre and auditorium are Grade One listed.
The South part of the river frontage comprises: three storeys and a basement with a two storey wing set back to the left with snecked grey rubble with long and short quoins, and freestone dressings to the windows. It has twin hipped slate roves with finials and a full-height castellated polygonal tower on the right corner. There are two two-light windows under the rectangular dripmould (wide inserted window on the right of the first floor). Pointed lancets are under the dripmoulds, which flank a four-light splayed bay with the entrance under this. There is a two-window left-hand section, with a gabled dormer and corner polygonal turret, with cross-loop windows, pyramidal roof with a weathervane. There is a low long wing to the service yard further left, with the front masked by a conservatory with Gothic upperlights.
The North part of the house comprises: three storeys and a basement, in red snecked facings with pale dressings. It is heavily castellated, with a central outlook tower over false machicolated battlements. There are two two-light Tudor windows with altered glazing. There are lower extensions to the right with parapets stepping down to a corner turret at a buttressed angle. The theatre extension, with a raised fly-tower, is on the North side of the house. The ashlar clock tower overlaps the corner of the theatre, with louvered bell-openings, a pyramidal roof with lucarnes and a weathervane. The main entrance in the front is in two parts with castellated detailing as before, with a lyre panel to the South block, an additional bartizan to the right corner, and a buttressed porch with an arched entrance. The two storey service wing is forward on the South side, with an arched entry to the courtyard under a steep hipped roof and stepped parapets to the gables.
The interiors retain the original plan form of the house, together with the original detailing including Jacobethan carving on the porch ceiling and a sequence of public rooms reached by a lateral arched corridor. The rooms include: a billiard room with a high coved ceiling; a music room with richly plastered ceiling and frieze; and a morning room with deeply coffered ceiling and unusual floral chimney-piece, with Walter Scott tiles. There is a full-width upstairs bedroom, formerly that of Adelina Patti.

The Castle included a gasworks, indicated by a gasometer marked on the 1887 to 1906 OS maps. The Castle was reputed to be the first house in Wales to switch to electric lighting c1890. A newspaper report from 1890 (The Cambrian, 22nd August 1890) explained that the theatre was lit by about 240 incandescent electric lamps of 8 and 16 candle power, the coloured light being produced by variously coloured glass bulbs, the rest of the castle was lit by gas as well, installed by the Wenham Company. The gasworks was used to supply gas to power a ‘Otto’ Gas Engine which was attached to a 110-volt DC generator which charges more than fifty large Faure accumulators, sufficient to keep the whole of the lights going for two nights. This supplied the house via two copper wires embedded in wood. The gasworks may have provided gas lighting prior to this.

Upon Patti's death the house was sold to Welsh National Memorial Trust in the 1920s and was used as a hospital until 1986, before being sold into private hands by the Welsh Office in 1988.
(Source 'Addition to CADW List of buildings of special architectural or historical interest, list No. 28, district of Brecknock')
Ian Archer, RCAHMW, 28th January 2005