There are many people from Wales - and visitors, too, come to that - who will swear that, standing on the cliffs of Cardigan Bay on a bright sunlit day, they have seen buildings shimmering under the waves. Or, walking the coast at dusk, to have heard bells ringing from far out under the sea.
Cardigan Bay (photo by Adrian Davies)
What they are doing is unconsciously tapping into one of the greatest of all Welsh legends, that of the lost kingdom of Cantre'r Gwaelod. The name means 'cantref of the low land' and if the story is even remotely true then the area was well named.
According to legend there was once a kingdom situated where Cardigan Bay now laps against the mainland. It was rich and well populated, boasting no fewer than 16 wonderful cities, communities full of merchants and princes.
But the kingdom was low lying and in order to protect the land a number of steep embankments or dykes had been built. These were regularly opened to allow water - for agricultural purposes and so on - to flood in. Only when the gates in the embankment, the sluices as they were known, were closed was Cantre'r Gwaelod fully protected.
The kingdom was ruled by Gwyddno Garanhir and he had delegated the working of the sluices to the control of a man called Seithennin. Normally fastidious in his duties, one tragic night of revelry saw Seithennin drink too much. Head reeling with the effects of the ale and wine, the unfortunate lock keeper stumbled to his bed and forgot to close the sluices.
With high tide the water poured into Cantre'r Gwaelod and, before anyone could come to the rescue or even give the alarm, the kingdom was lost forever under the waters of Cardigan Bay. So much for the legend.
Both Gwyddno Garanhir and Seithennin are referred to in The Black Book of Carmarthen, the earliest written collection of Welsh verse, dating from the middle years of the 13th century. Several of the poems come from a much earlier time.
That does not necessarily mean the legend is true, simply that, by the 13th century, it was common knowledge and that the tale seems to have fairly ancient roots. Similarly, one of the stories in the Mabinogion refers to the drowning of the kingdom that once lay between Wales and Ireland.
Like all legends, trying to separate fact from fiction is devilishly difficult. On one level the story may simply be a parable or tale invented by the bards, one that has a moral to pass on to ordinary folk - always be prepared, do not over indulge and so on.
On the other hand, the story of Cantre'r Gwaelod may well be the remnants of a folk memory concerning the inundation of land around Cardigan Bay.
There is evidence, in the form of ancient drowned forests at places such as Newgale and Ynyslas, that when the ice sheets from the most recent Ice Age finally retreated much land was lost to the sea. This was about 8,000 years ago and was a time that saw the oceans reach their present level.
There is no record of cities and cantrefs being swept away but land did disappear under the waves during this period. It is only a step away from such historical fact to the concoction of legends such as that of Cantre'r Gwaelod.
The early travel writer and author Giraldus Cambrensis wrote about the drowned forest at Newgale. His writings and the famous Welsh folk song The Bells Of Aberdovey, which supposedly refers to the story of Cantre'r Gwaelod, have helped keep the legend alive.
So the next time you are standing on the cliffs above Cardigan Bay narrow your eyes and peer out towards Ireland. Or, on a calm and still night, listen for the pealing of bells from somewhere deep below the sea. It may be your imagination at work but, then again, it might just be the lost kingdom of Cantre'r Gwaelod calling out to you.