Holy Trinity Chapel was begun by Sir Richard Wynn, 4th Baronet of Gwydir, in 1673 as the private chapel to Gwydir Uchaf. Built chiefly in yellow sandstone ashlar with a roof of thick slates, the chapel has a rectangular form with no formal division between nave and chancel. There is an original gabled bellcote at the western end, though the bell itself is dated 1752.

Beneath the plain and almost Gothic exterior, lies an almost 'High Church' interior that flies close to catholicism. Indeed Sir Richard consulted a Jesuit, Father Edward Petre, over `procuring a Cross', a stained-glass Crucifixion. The interior is largely preserved from the seventeenth century. It is dominated by an elaborate firmament ceiling with sun, moon, stars, figures of God the Father, doves, cherubs and demi-angels with inscriptions, and has a gallery supported on a large beam embellished with carved and brightly painted decoration. There are also finely carved lime wood cherubs affixed to a number of the corners of the wood panelling which adorns the chapel walls. A framed panel bearing the arms of Charles II is fixed to the south wall.

Regular services continued in the chapel until circa 1920.

Sources include:
Haslam, Orbach and Voelcker (2009), The Buildings of Wales: Gwynedd. Pevsner Architectural Guide, page 380
Yates, W. Nigel. (2005) Rug Chapel, Llangar Chruch, Gwydir Uchaf Chapel & Derwen Churchyard Cross: Cadw Guide (Revised Edition)
Richard Suggett, Painted Temples: Wallpaintings and Rood-screens in Welsh Churches, 1200–1800, (RCAHMW 2021), pp. 261, 262–66, 278, 282.

RCAHMW 2021