Not many capital cities can lay claim to have been the home of a cryptid. On occasion fortean zoology and related subjects will crop up in the founding myths of the great cities of the world (such as Rome's origin myth where it's founder and his brother was raised by a wolf) on occasion or as protectors of cities and countries; for example, the head of Brân the giant protecting Britain from invaders. But one cryptid said to have made its home in the Welsh capital of Cardiff was a bit different.
The Cardiff Winch Serpent had nothing whatsoever to do with the city's founding and was the certainly not a protector of its people. The Great Snake was said to have made its home in the River Taff and would coil and uncoil its gargantuan body underwater to create a treacherous whirlpool, drawing unsuspecting swimmers and boats into its watery larder to feast upon. According to some accounts the serpent was aided and abetted in this endeavour by a beautiful woman. In the words of the folklorist Marie Trevelyan:
“An old woman who was fond of telling nursery stories related to her by her grandmother said that the Taff whirlpool was frequented by a lovely lady, who lured people whilst bathing. Youths were known to swim or row towards her, attracted by her beauty. They were then sucked into the vortex, and their bodies could never be found, said the narrator, "and it is fathomless. It reaches from the Taff to the mouth of perdition, where Satan waits for the souls who are beguiled by the lovely lady." She said the lady was the devil in disguise. "It is a dreadful winch," in Wales the word "winch" is always associated with water.”
It is up for debate who the originators of this tale were; it may well have been concerned parents wanting to keep their children from swimming in treacherous waters as with other tales of Winch Serpents from Wales such as in the Great Gutter by the Nash Sands or the Kenfig Pool near Porthcawl. But the additional detail in this case of swimmers being lured out by a good-looking moist lass suggests it may have been intended to ward off a slightly older audience in this case. It is interesting to note that the Winch Serpent was said to frequent an area of the Taff a little way to the south of the pirate dock.* Pirates attempting to scare people away from their section of the Taff could be a plausible source of the stories.
If you want to visit the approximate site of the Winch Serpent's whirlpool for yourself it is quite easy to do. Simply get off the train at Cardiff Central station and head in the direction of the Millennium Stadium. Because this part of the Taff was filled in and re-routed to drain the marshes the station was to be built on you'll have to walk up the non-Taff side of the stadium. Eventually, after passing the old customs house, you'll come to a junction by a multi-story carpark. As you stand near the gates of the stadium here you will be standing roughly where the pool was.
*(interesting fact while I think of it: you know the generic pirate accent you hear in films? That was actually based on a really bad amalgamation of both a Cardiff and Bristol accent by the first actor to play Long John Silver in a talkie version of Treasure Island. These days, however, few people even know that Cardiff had at one time the largest pirate dock in Europe so good the pirates were at bribing and threatening the authorities)