When I visited Worm's Head earlier this year it was a bright but cold and very windy day. I viewed the surrounding coastline (with binoculars) and could see no obvious 'lumps and bumps'. There is a pay-and-display car park, cafe and N.T. shop.
Baring-Gould says "There can hardly be a doubt that by Henisweryn the Worm's Head Island is intended" (he explains in detail why he thinks so)
The story's of Saint Cenydd's a bit long (and this is only the start) - but as BG says, "It is a most extraordinary tale, a mass of fable. It was certainly composed after Geoffrey of Monmouth had made the fortunes of King Arthur, i.e. 1150. That it contains earlier matter is not to be doubted; not of an historical, but of a mythological character."
In the days of King Arthur, the prince of Letavia (Llydaw) or Britannia Minor, was Dihoc, and he became the father of Keneth, who was born of incest. Summoned by King Arthur, as a tributary, to come to his court to celebrate the Feast of Christmas in Gower, he took with him the woman, and she gave birth to a child, who was born a cripple, with the calf of one leg attached to the thigh.
Dihoc ordered the infant to be thrown into the river, but before this was done, a priest baptised it and gave it the name of Keneth. The child was placed in an osier-woven cradle and launched on the stream. This stream speedily carried it down to the river Lothur, and that swept it out to sea. A storm arose and drove the cradle, dancing on the crest of the waves, to the isle of Inisweryn, where it was cast up on the beach. At once a cloud of seagulls fluttered over the child, and the birds with beak and claw removed it to the top of a rock, and there they strippped their breasts of feathers to make a bed for the infant. The birds kept incessant watch over their protege, spreading their wings over him to shelter him from wind and rain and snow.
Before nine days had passed, an angel descended from heaven, bearing a brazen bell, which he applied to the mouth of the infant, who sucked vigorously at the handle, and received therefrom much satisfaction.
Certain practical difficulties, such as would suggest themselves to a mother, are got over by the author with an ingenious explanation.*
Thus Keneth lived till he was able to walk, and the garments in which he had been wrapped when exposed, grew with him, expanding, as does the bark of a tree.
One day, a peasant who lived near the sea, and who had no family, happening to light on the child, took it up and carried it home, and committed it to his wife, who at once put the little Keneth to bed. This caused tremendous excitement among the gulls; they came in vast numbers, and dividing into two bands, one entered the house and pulled the coverlet off the sleeping child, and the other, with screams and by the aid of beak and claw, drove the cattle of the husbandman towards the sea.
The man, alarmed for his live-stock, hastily carried back Keneth to where he had found him, whereupon the gulls drove back his cattle to their pastures, and, in the most tidy manner, replaced the coverlet whence they had plucked it.
And now daily a female stag came out of the forest, and squirted her milk into the bell that Keneth employed as his feeding-bottle, and likewise filled some hollows in the rocks hard by.
It goes on a bit as you can imagine, and you can read the rest here in Baring-Gould's 'Lives of the British Saints' (1907). It's got such curious and celticky detail, with all those helpful animals.
*Here there's some Latin which Google translate tells me means the child did not poo. Clearly too rude to write in English for a vicar. But incest and child murdering is ok.
Camden, in his "Britannia," informs us, -- "In a rock in the island of Barry, in Glamorganshire, there is a narrow chink, or cleft, to which if you put your ear you shall perceive all such sorts of noises as you may fancy smiths at work under ground, strokes of hammers, blowing of bellows, grinding of tools." At Worm's head, in the peninsular of Gower in Glamorganshire, these sounds are, even now, often heard; and it requires but a moderate stretch of imagination to create all this cyclopean imagery, when the sea is rolling in cavities under our feet, and the tone of its voice is magnified by confinement and repercussion.
From p151 of 'The Philosophy of Mystery' by Walter Cooper Dendy (1841).
I've since found out it wasn't Camden at all - it was Giraldus Cambrensis:
.. In a rock or cliff, by the sea=side in Glamorganshire, near the Isle of Barry, there appeareth a little chink, into which, if you lay your ear, you shall hear a noise as of smiths at work - one while the blowing of bellows, another while striking of sledge and hammer, sometime the sound of the grindstone and iron tools rubbing against it, the hissing sparks also of steel gads within holes as they are beaten, yea and the puffing noise of fire burning in the furnace. Now I am persuaded that the sound comes of the rush of the sea water.
Sounds far too complicated for that. But you could be right.