A cave located on the north-west side of Dinas Hill near Ystrad-ffin (NPRN 17928) reached by a steep ascent. The name of the cave derives from the Welsh trickster, highwayman and folk-hero, Twn Sion Catti who is supposed to have hidden in the cave while wooing the widow of nearby Ystrad-ffin farm and again when escaping from Llandovery fair (see Prichard 2017, pp. 168?70, 185?6). The cave was described in Thomas Prichard's The Adventures and Vagaries of Twm Shon Catti (org. pub 1828) at some length, implying that the author was familiar with the site:

`A narrow valley circled its base and the mountains around of equal height with itself, separated only by this deep and scanty dell, seemed as if rent from it, during the supposed convulsion of the earth, and Dinas left alone, an interesting monument of the memorable event. The surface of the acclivous ground was so speckled with huge loose stones that it was dangerous to hold by them in ascending, as the slightest impetus would roll then downward.
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`The entrance into this excavated work was no less singular than the petite cave itself, it was through a narrow aperture, formed of two immense slate rocks that faced each other, and the space between them narrower at the bottom than the top so that the passage could be entered only sideways with the figure inclined forward, according to the slant of the rocks, a thin person being barely able to make his way in, while a man of some rotundity might also succeed by rising on his toes and forcing himself upwards. Between these rocks of entrance a massive stone block was wedged at the top so that it formed a rude and comparatively long passage, it was no small surprise to find that it led to so small a cave; scarcely large enough to shelter three persons huddled together from a shower of rain. What I wanted in breadth it possessed in height, as it ran up like a chimney to the altitude of forty five feet and was open at the top to the very summit of the mount, forming a skylight to the room below. Although the little cave was deficient of a solid roof, a very rural one was formed by the large tufts of heather an fern, which sprung through the crevices of the rocks; the whole being surmounted by the pendant branch of a dwarf oak what with many other trees stood like a crown on the elevated head of Dinas.? (Prichard 2017, pp. 169?70)

The cave became a popular tourist destination during the nineteenth century, visitors journeying to it, as Twm had supposedly done, from Ystrad-ffin Farm. It is now part of the Gwenffrwd-Dinas RSPB reserve.

(Sources: T. J. Llewelyn Prichard, The Adventures and Vagaries of Twm Shon Catti Descriptive of Life in Wales, Interspersed with Poems, ed. by Rita Singer (Aberystwyth, Llyfrau Cantre'r Gwaelod, 2017); Roger Worsley, `Twm Sion Catt and the First Welsh Novel?, Carmarthenshire Life, May 1997, 14?15; Meic Stephens (ed.), The New Companion to Welsh Literature (Cardiff: University of Wales Press: 1998), s.v Twm Shon Catti, p. 742; RSPB website)
A.N. Coward, RCAHMW, 07.01.2019