Abereiddi is a hamlet in the county of Pembrokeshire, in south-west Wales.
It has a small beach which was awarded the Blue flag rural beach award in 2005. A large car park adjoins the beach, where in the summer an ice cream van can usually be found. The beach also has public toilets which are open from Easter to October half-term. The Pembrokeshire Coast Path gives fine walking in both directions. The Common which runs inland behind the beach lies within the Manor of Llanrhian.
Following the coast path north leads to Porthgain. Abereiddi to Porthgain is roughly a forty-minute walk.
The coastal path taken in the other direction to the south east goes around St Davids Head and on to Whitesands Bay.
Nearby are the ruins of the 'Blue Lagoon', a small slate quarry, now flooded by the sea having broken in. Initially slate was exported across Abereiddi beach, but later through a tramway to the harbour at Porthgain a couple of miles to the North. Although never as large a quarry as even those nearer Porthgain itself, it did operate a steam-hauled lift.
Ruins of a small group of slate houses known as The Street remain near the beach. These were houses built for the quarry workers of the Blue Lagoon and was only abandoned after a flood in the early 20th century.
The Blue Lagoon is 25m deep, according to a nearby Pembrokeshire National Park information board. Despite the name, the water is always a distinct greenish hue, owing to the mineral content within the quarry. The lagoon is a favourite for adventure groups practising coasteering, and also diving when the weather is bad.
In September 2012 the Blue Lagoon at Abereiddi was the location for one of the stages of the Red Bull Cliff Diving World Series, making its UK debut. Fourteen of the world's best divers dived from a man-made platform, 27 metres above the Blue Lagoon.
The championships were held here again in September 2013.