In the 20th century, the modern town developed rapidly to accommodate Royal Air Force personnel from the St Athan base.

Colhugh Beach is a popular surfing venue and has the remnants of an Iron Age fort and some of Wales' finest examples of Jurassic Period fossils.

The pebble beach and its clifftops are protected as part of the Glamorgan Heritage Coast, which stretches for 14 miles (23 km) from Gileston to the east to Southerndown and Newton Point to the west.

The Welsh place-name element llan[5] referred to the sanctified community around early Christian settlements in Wales and its parish rather than merely the church itself (eglwys).

Records from 1893 suggest that one room was used as a praetorium, another as a workshop; and there was a 5th-century adjoining sacristy, simple in style, which featured a chancel, nave, and stone altar.

A record from 1907 described the relics as Samian ware pieces; bronze coins of Maximinus Thrax, Victorinus, and Constantius Chlorus; as well as roofing materials.

By the 4th century, there was an L-shaped villa with a large, aisled building possibly for farm workers, and a number of smaller agricultural structures almost enclosing a central courtyard.

The Royal Commission on the Ancient and Historical Monuments of Wales has associated collection records of the site, including drawings of other remains such as statues and a tessellated pavement, as well as documentation of a 1971 excavation.

[11] Germanus of Auxerre and Lupus of Troyes made at least one visit to Britain in AD 429 and founded or refounded a number of ecclesiastic establishments across South Wales.

[12][13][14][15] Under Illtud and his successors, Bangor Illtyd and the monastery grew in reputation both as the origin of many prominent Celtic evangelists and as a major centre of scholarly education.

[16] The college itself was said to be the oldest in the world, consisting of seven halls, 400 houses and more than 2,000 students at its peak,[17] including seven sons of British princes, and scholars such as St. Patrick, St. Paul Aurelian, the bard Taliesin, Gildas the historian, Samson of Dol, and St. David are believed to have spent some time there.

[22][23] In the 20th century, Llantwit developed into a dormitory town and grew about 15 times in size to accommodate the Royal Air Force at St Athan.

[13] Despite its modernization and rapid growth, it retains its pre-modern feel with its narrow winding streets, high walls, old town hall and gatehouse, and several inns and houses dated to the 16th century.

At the lower coastal level is the flat, glacial Colhugh Valley, marked by steep cliffs on both sides, leading to a pebble beach.

[27] The beach, located to the south of the town (51°23′48″N 3°30′03″W / 51.396667°N 3.500833°W / 51.396667; -3.500833), has the remains of an ancient old stone wall from the large Iron Age hill fort, Castle Ditches.

The steep cliffs at Llantwit which allow walks along the coast to St Donat's Castle and Atlantic College have undergone dramatic erosion in recent years: in many places, the rock structure has collapsed in piles, particularly on the eastern face.

The cliff path, once set about 100 yards (90 m) from the edge is now within metres of the nature pathway, and the Vale of Glamorgan Council has installed extensive new barriers to prevent fatalities.

The 14 miles (23 km) of coastline from Gileston in the east to Newton Point in the west, passing through St Donat's and Southerndown, is protected as part of the Glamorgan Heritage Coast.

[28] Llantwit Major beach has one of the finest sites in Wales for Jurassic fossils, including corals, giant brachiopods, gastropods and the bones of Ichthyosaurus.

The beach has a snack bar and restaurant and associated amenities to cater for the increased public demand in recent years.

There is an expansive rocky beach at low tide, with a stretch of sand towards the far west, and views of the Bristol Channel and the coastline of Somerset, with the landmark white roof of Butlins, Minehead.

The beach has a lifeguard station funded by the Vale of Glamorgan Council, built in the late 1990s, functioning during the summer months.

[35] Manorial records indicate that the Town Hall (51°24′27″N 3°29′05″W / 51.4076°N 3.4848°W / 51.4076; -3.4848) dates to the 15th century but it is often attributed to Gilbert de Clare, Lord of Glamorgan, who died much earlier in 1295.

[13] The Williams family were successful lawyers and part of the rising minor gentry who were loathed by the Seys of Boverton and the Stradlings of St Donats.

Vann was fined over £1,000 for being involved in a scuffle in central Llantwit on a Sunday which led him to take on the Sey family and seek his revenge.

[37] Later owners included Daniel Durrell, headmaster of Cowbridge Grammar School, and the benefactor of Tabernacle Chapel, Elias Bassett.

[50] The old police station (51°24′25″N 3°29′14″W / 51.4069°N 3.4872°W / 51.4069; -3.4872) was built in the mid-1840s after the place is Glamorgan Constabulary was established in 1841, and was originally comprised a single-storey building, but was expanded in 1876 to include four bedrooms on the top floor.

[51] It was built at the end of the 16th century and served as the seat of Roger Seys, Queen's Attorney to the Council of Wales and the Marches in the 1590s.

Robert Carne, at the end of the 18th century, upon land left him by his father, Whitlock Nicholl of The Ham, sheriff for the county of Glamorgan in 1746.

The dwelling is of castellated Tudor architecture with blue lias limestone exterior, and Coombedown stone windows and cornices.