Good clue and nice to see something a bit different.I hope I got the apostrophe in the right place, it was inteded to indicate a plural possessive. Scarlet on its own is vague, but Scarlets as a plural is rare. I believe Grahams worked this out as he suggested a Gower cave - south of the home of the Llanelli Scarlets, one of the four Welsh rugby regions.
If you look south from Llanelli, you look over the wide expanse of the Lougher estuary. The source of the Lougher is Llygad Llwchwr, where the water comes out from the rock at a site that literally tramslates as the Eye of the Lougher.
...anyway Robin got it...