Question about Wales

[Thanos6]

OK, so I have the collected volumes of an old partwork, The Unexplained/Mysteries Of Mind, Space & Time. It's all about the paranormal. I don't believe much of it, but it's unbeatable for story ideas.

There's a recurring feature in it called "The World's Mysterious Places," which are just photographs of, well, mysterious places. Stonehenge, the Pyramids, etc.

Several of them I'd never heard of, but some research enlightened me. However, there's one place where even research hasn't helped me.

This is Swallow Falls, Bettws-y-coed, Wales. I haven't been able to find out what makes it "mysterious." It just seems like an ordinary waterfall, with no legends or anything surrounding it.

Can anyone who knows about this help a poor Yank out?