SOUTHERNDOWN, a hamlet, in the parish of ST-BRIDE'S-MAJOR, hundred of OGMORE, county of GLAMORGAN, SOUTH WALES, 5 miles (S. by W.) from Bridgend; containing 813 inhabitants. This place is situated on the sea-coast, and comprises the southern declivity of a very extensive down. Close to it, on a 'small promontory, presenting rocky and lofty cliffs, stands DP unraven Castle, once the seat of Thomas Wyndham, Esq., who erected the present spacious and elegant structure, in the early Entglish style, on the site of a more ancient castle, said to have been the oldest in Wales, and once the residence of the celebrated Caractacus, as well as of his father, Bran ab Llyr. It continued occasionally to be the seat of the reguli of this district after the capture of the British hero, and until the Norman conquest of Glamorgan, in the time of Iestyn ab Gwrgiut, when, on the partition of that territory by Robert Fits-Hamon, the castle and manor were assigned to William de Londres, who bestowed them on his butler, afterwards Sir Arnold Butler, one of whose female descendants conveyed them by marriage into the family of the Vaughans, from whom they were purchased by an ancestor of the late Mr. Wyndham, whose only daughter and heiress conveyed them by marriage to Windham Henry Wyndham Quin, Earl of Dunraven and Mountearl: the castle is now the residence of Viscount Adare, M.P. A lofty embankment across the peninsula, still traceable, protected the castle on the land side, while the bold cliffs rendered it inaccessible from the sea. About a mile westward from it are three very extraordinary natural caverns, formed by the action of the sea on the projecting rocks. One, termed by pre-eminence "the Cave," is approached from the south by a rude piazza worn through the rock, the appearance of the sea and sky between the rough arches of which has a grand and singular effect. The next is a cavern called the " Wind hole," extending about twenty-seven yards, with two or three fissures in the roof, at a considerable distance from the edge of the cliff; and if a hat or any other light substance be placed on the opening on the top, it will be violently blown into the air. The third has received the name of the " Fairy Cove," from the number of petrifactions it contains, which have assumed such a variety of grotesque shapes as to be considered the most curious of the whole. At the western end of the down, which abuts on the Ewenny river, is another singular object, consisting of a large body of water issuing from the bottom of the down, which foams and boils with much force, and forms two small streams.