Abereiddi & the Blue Lagoon

Abereiddi's little black-sand beach (the colour comes from crushed slate) would be a curiosity on its own; what makes it famous is the Blue Lagoon next door — a 19th-century slate quarry breached by the sea, now a deep, uncannily blue-green pool ringed by ruined quarry buildings. It's the signature venue for guided coasteering (book with a licensed St Davids operator; don't jump unguided — depths and swell are deceptive) and hosted Red Bull cliff-diving championships more than once.

Fossil hunters split shale on the beach for graptolites; walkers carry on to the ghost quarry village at Porthgain, twenty minutes up the Coast Path, where the Sloop Inn and the Shed bistro make the best short walk-and-lunch circuit on the north coast.