At its peak in the 14th century the Cistercian abbey at Neath was the largest in Wales, and its ruins are comparable in grandeur to those of the better-known Tintern Abbey in Monmouthshire, although they are less complete, and the setting is not so dramatic. Like Tintern, and all similar Catholic establishments, the abbey prospered for several centuries until closed as part of Henry VIII's Suppression of the Monasteries, in 1539. Some of the outbuildings were converted to a mansion in the 16th century, though this too is now ruinous, albeit somewhat more complete than most of the remainder.
The abbey was centred on a huge, Gothic church, 250 feet long and at least 80 feet high, adjoined, to the south, by a rectangular cloister lined on the other three sides by monastic buildings, including a chapter house, refectory and dormitory, while further southeast was another group of rooms. When built, the monastery was surrounded on all sides by open fields, which in turn were enclosed by a low wall, entry being through a gatehouse to the north, 600 feet from the church, but now all the neighbourhood is developed. Part of the gatehouse survives, along the main road through the western suburbs of Neath, while the abbey sits next to several modern buildings including a car dealership, which detract from the overall appearance and atmosphere, and since 2014 parts of the site have been fenced off, on account of a long lasting renovation project caused by a combination of floods and frosts. The whole site is similar in completeness to Glastonbury Abbey in Somerset, and while the outbuildings do not match those of this and some other abbeys in terms of ornateness and architectural style, the place as a whole is extensive and still impressive.
Neath Abbey was established in 1129 on an 8,000 acre site within the lands of Richard de Grenville, one of the twelve knights of Glamorgan, and was initially staffed by monks from Savigny Abbey in Normandy. The place flourished for over 400 years, though its peaceful existence was interrupted several times by Welsh uprisings, during the 13th and 14th centuries, which necessitated various rebuilding works, including replacement of the initial, rather modest church with a much larger one, between 1280 and 1330. After the dissolution, the site was acquired by Sir Richard Williams alias Cromwell, and he (or his son) converted part of complex to a mansion, retaining some original components including the monk's day room and undercroft. The mansion was occupied for around 200 years and later saw use as a copper smelting workshop, before laying derelict for a time. It was partly restored at the start of the 20th century.
The monastery is part of the village of Neath Abbey, on the west side of Neath, and is built on the west bank of the River Clydach, close to the confluence with the larger River Neath. The south edge of the grounds adjoins the Tennant Canal (constructed 1818), and the north side is bordered by a railway line, built in 1863. The access road is along the west side; a quiet, dead-end side street branching south off the A420. The remaining section of the gatehouse is along the main road, and it consists of two arches plus a section of wall, enclosed by railings, and now incongruously situated beside a nursery and some houses. Parking for the abbey is along the approach road. Entry is free and the site is sometimes staffed; entrance is through a gate at the southwest side of the complex, next to an administration building.
The approach path passes the south end of the west range, which is the oldest part of the site, built at the end of the 12th century: this consists of two main rooms, the lay brothers' refectory and lay brothers' common room, separated by a ground floor passageway, opening on the west side to a porch with an arched doorway. The east side of these rooms borders the cloisters, and wall foundations indicate there were two parallel corridors here; the other three sides of the cloisters had just the usual single corridor. The south range consisted of the kitchen, monk's refectory and warming house, though most of the walls of these are missing, or survive only as foundations. The northern part of the eastern cloister adjoins the south transept of the abbey, beside which are two small enclosures, the book room and the sacristy, both of which have nearly full height walls, while further south was the square, vaulted chapter house, little trace of which remains, and then the parlour and a corridor. Southeast of here were several other rooms including the monk's latrine, monk's dormitory and monk's day room, most of which were incorporated into the mansion built in the mid 1500s. The ruins of this structure have been the main focus of the renovation project started in 2014.
The great abbey church has the familiar cruciform design, with the nave to the west, leading to the choir and presbytery, these enclosed by low internal walls, and all lined by full length aisles, with north and south transepts at either side. Most of the walls of the nave survive to clerestory level, and incorporate several huge window openings, while part of the west front is significantly higher, with two full height columns either side of the space occupied by the main window. The presbytery, the choir and two sets of three pillars either side of the nave are now just foundations, but the two transepts also have some tall wall remnants, and arched windows. The east end of the church is the least complete section, and around here (and the north transept) are some huge fallen blocks of masonry, still with recognisable features such as arches and vaulting, left here since destruction following the 16th century dissolution; suggesting that the place was deliberately ruined rather than simply left to decay. Other architectural features of note include the lower section of the night stairs (to the monk's dormitory) in the south transept, the lower halves of a pair of elaborate fluted columns either side of the main doorway to the church from the cloisters, and some original, decorative floor tiles in the mansion.