Trefeilir is an eighteenth-century house near Trefdraeth, Anglesey. The majority of the extant structure of the building was constructed in 1735, incorporating the remains of a sixteenth-century house, representing all that remains of an earlier building, into one wing of the property. Inside, key architectural features include two sixteenth century fireplaces and the main staircase. The staircase is a `Chinese? staircase, and was probably added to the house in c. 1760. It is possible that the new staircase was added to the house in preparation for the marriage of owner Charles Evans (1726 ? 1802) to Elizabeth Lewis (1740 ? 1805) in 1761. The site file notes that `other? contemporary renovations to the interior of the building, in addition to later modernisation work, were so extensive as to completely obscure the original sixteenth-century floor plan.

The `Chinese? staircase appears to be made from dark wood, and has a reasonably plain handrail, newel and newel cap. The tread ends are carved with a stylised wave design. The staircase ascends from the central hall to the first floor in two flights, with different sequences of patterns used for each flight and the landing.