A Cistercian monastery was established at Margam, now near the south edge of Neath Port Talbot, in 1147, and like all other such Catholic establishments, it flourished for several centuries until an abrupt closure in 1536, as a result of Henry VIII's Suppression of the Monasteries. The usual fate of such places was either to become ruined, and dismantled, or for some part to be retained, used as a parish church or as a residence. Both outcomes happened at Margam; the nave of the abbey was converted to a parish church, still in regular use, while the remainder of the abbey and all its outbuildings were either removed or left to become ruined; this followed the sale of the site, to Sir Rhys Mansell (1487-1559), High Sheriff of Glamorgan, and owner of Oxwich Castle. He constructed a grand mansion on the south side of the church, retaining only a small part of the associated buildings. The estate later passed to the Talbot family, who demolished the mansion and replaced it with an orangery, a handsome structure that survives today.
The surviving ruined sections of Margam Abbey are much smaller than some others in south Wales like Tintern, or nearby Neath, but are no less atmospheric. The largest building is the 12-sided chapter house, which has full height walls and the lower part of the central column, the vaulted ceiling having collapsed over 200 years after the suppression, in 1799. The doorway adjoins a short section of the cloisters together with a particularly ornate triple-doorway entrance on one side, while to the south is part of the undercroft, once supporting the monk's lodging. On the other side are a few low walls and column foundations from the east section of the original church.
The parish church is free to enter, and despite various later modifications, it retains many Norman features including most of the west front, but more interesting are the other monastic remains, which despite being right next to the church fall within Margam County Park, to which an entrance fee of £5.40 per vehicle is charged. Although all the ruins can be seen in just half an hour or so, the surviving sections are well-preserved and the site is most evocative. Nearby, also in the county park, are two other historic buildings, both much more recent; the orangery, and Margam Castle (a Gothic mansion), from the 18th and 19th centuries respectively, while the park also contains woodland, pathways and a lake, but the abbey ruins are certainly the most interesting attraction.
The church and the county park lie just east of the M4, reached from exit 38. The church is at the end of a short side road that passes a few houses and leads to a parking area in front of the graveyard. To the left is the Margam Stones Museum, a former schoolhouse that contains a collection of around 30 ancient religious stones, some Celtic, others Norman, all found in the vicinity. The collection was assembled by the Talbot family, who inherited the site in 1786. The museum is separated from the abbey by the extensive graveyard, which extends around the north side of the church and is bordered by a high wall at the far side; the land beyond is part of the county park, the entrance to which is one mile away by road, along a track to a parking area in front of the visitor centre and fee station. Paths lead to the abbey ruins, the orangery, the castle and various other sites.
The church (officially the Abbey Church of Saint Mary the Virgin), one of two serving Margam parish, occupies the westernmost six of the original eight bays of the nave of the monastic church. The structure has been modified several times since the dissolution, after becoming partially ruined in the 18th century; the largest unaltered section of the exterior is the centre of the west front, containing a fine, recessed doorway lined by concentric rows of carved mouldings, with narrow vertical buttresses at either side, and three elegant, arched windows above. The north and south wings and the Italianate towers above the buttresses were added in the early 1800s along with the uppermost section of the walls, part of modifications which included lowering of the roof and removing of the clerestory windows. Inside, the church has two aisles, separated from the central area by the original Norman rectangular piers, and is illuminated by three Victorian stained-glass windows at the east end. Most of the interior decor is from the late 19th century.
Apart from the church, the largest surviving component of the abbey is the dodecagonal chapter house, its walls about 30 feet high and centred on a slender column topped by the lowest section of the ribs that once supported the vaulted ceiling. This collapsed due to a series of hard frosts, having been weakened by the removal of its protective lead covering, for use in the neighbouring mansion. The entrance to the chapter house is on the west side, from the vestibule, a twin-passaged enclosure between the south transept of the abbey to the north, and the eastern cloisters to the south. Entrance to the vestibule, from the west, is through three decorative, arched doorways that originally opened to the central cloister garden. Nothing remains of the rest of the cloisters apart from a few column foundations. Most of the south range is now the site of Margam Orangery, built in the 1780s. Fragmentary remains of the remainder of the church are some low wall sections on the south side, including two doorways, a higher part of the walls of the south transept, and minor foundations to the north. The only other structure is the undercroft, a vaulted enclosure of three bays that once supported part of the monk's dormitory.