Seion Welsh Wesleyan Methodist Chapel was built c.1804 for a cause founded in 1791. It was later rebuilt/modified in 1841, before being enlarged in 1860 and 1870, and rebuilt on two further occasions in 1877/8 and 1905. The current chapel is in the Gothic style, constructed of red brick with freestone dressings beneath a pitched slate roof with slightly overhanging eaves. The gable facade of the chapel has three bays, the central of which is divided by buttresses which rise to form turrets, and has paired Gothic doorways with overlights, flanked by lanet windows, with a pair of large two-light windows with septfoils above, and a further septfoil in the gable apex. The outer bays have a variety of lancet windows, while the side elevations have paired lancets on the ground floor, and two-light windows on the gallery level with roundels above.
Within the chapel is a three-sided gallery wit panelled front mounted upon cast iron columns with fluted capitals. There are four sets of box pews below, forming two aisles, facing the panelled pulip and set fawr.

Source: RCAHMW Inventory Documents

K Steele, RCAHMW, 24 March 2009