Porthgain and the Blue Lagoon

Two industrial ruins on the north Pembrokeshire coast of Wales have become the most beautiful stretch of the coast path. At Porthgain, brick hoppers the size of houses loom over a harbour that once loaded crushed granite into ships; at Abereiddi a slate quarry pit breached by the sea has become the Blue Lagoon, 25 metres deep and green as bottle glass.

The name means chisel port: from around 1850 the village shipped slate, then bricks from the Ty Mawr works, then road stone crushed from the tiered quarry along the cliff, dispensed from the hoppers built in the early 1900s straight into the holds alongside the quay. The work ended in the 1930s and the village kept its shape: the Sloop Inn of 1743, a café-restaurant, art galleries, and boats that still use the harbour. The circular walk to Abereiddi and back is around 3.6 miles, past Traeth Llyfn, a beach of extraordinary rock formations reached by steep metal steps and cut off in parts at high tide, to the lagoon, where the ruins of the engine house overlook the pool and a slipway lets small boats in. The Blue Lagoon is a flooded quarry, not a beach: the national park warns of currents and undertows, and in autumn access is often closed to leave the seal pups alone. Abereiddi's own beach is black sand, with tiny fossil graptolites in the shale; together they are the Pembrokeshire coast at its most surprising: the industrial past not tidied away but turned into the view.