An old slate quarry on the north Pembrokeshire coast, flooded when the seaward wall was breached and now a deep pool of startlingly coloured water, ringed by the ruins of quarry buildings. It is used for coasteering and diving; swimming here needs care. It is a short walk north from the beach at Abereiddi.
Blue Lagoon, Abereiddi
Flooded slate quarry open to the sea at Abereiddi, deep and startlingly green-blue
Most visitors miss this
At Abereiddi you can take in the so-called Blue Lagoon (pictured above and below), which was created when the wall of an old mine was demolished.