After having a rather nice lunch in the pretty market town of Cowbridge, I managed to pursuade Karen that a slight detour on the way home would do no harm! Travelling west out of Cowbridge, take the turning south signposted Colwinston. Immediately after the turuning park as best you can near Twmpath house. The Barrow is in the trees to the left of the drive.
Covered in brambles, nettles, ivy and trees the Barrow is not that easy to spot but appears to be about 0.5 metres high and about 10 metres across.
Not worth making a special journey for but wortha quick look if in the area.
Coflein describes the site:
A much disturbed and mutilated round barrow, about 27m north-east to south-west by 20m and 1.4m high: excavations through the 19th century demonstrated that the mound, originally about 17.7m in diameter and 1.5m high, contained 13 in-urned cremations placed in a central drystone-walled enclosure; there were also five secondary burials.
A remarkable tumulus known as the Twmpath, near Colwinston, was thoroughly explored under the direction of Mr. F. G. Price, F.S.A., in 1887. The central portion had been excavated several years previously by the then owner of the property, when nine cinerary urns and their contents were brought to light; but as these were not the sort of treasure he looked for, the work was abandoned.
[.. Price] mentions the tradition of a local battle, the slain of which were said to be buried here.
From a 'Handbook to Cardiff and the neighbourhood' from 1920, here.