Blue Lagoon
St David's Pembrokeshire
The Blue Lagoon is a former slate quarry that has been flooded by the sea and has improbably turquoise blue waters – into which thrill-seekers fling themselves from various heights up the quarry walls. It’s also a fine coasteering venue and nearby Abereiddi Beach gets decent surf from time to time. It's a National Trust coastline, with a great walk in on the Pembrokeshire Coast Path National Trail.