Cefn Sidan, translated from Welsh, means "Silky Back". This long sandy beach and its dunes form the outer edge of the Pembrey Burrows between Burry Port and Kidwelly, facing southwestwards over Carmarthen Bay in South Wales. Cefn Sidan beach is backed by dunes, salt marshes, Pembrey Forest and the Pembrey Country Park.
Pembrey beach stretces for nearly eight miles from the coastal town of Burry Port to Tywyn Point at the mouth of the Gwendraeth estuary near Kidwelly. The sand has small grains and the beach is backed by dunes of windblown sand. There are sand bars projecting as shoals into Carmarthen Bay at either end of the beach. The beach has a life guard patrolling during the summer months and can be accessed by ten approach routes where notices provide information for visitors. Pembrey Forest, the Saltings nature reserve and Pembrey Country Park are inland from the beach, and RAF Pembrey is also sited here.
The sands were treacherous to sailing ships and a number of vessels were certainly lost around Pembrey, including "La Jeune Emma" bound from the West Indies to France and blown badly off course in 1828. 13 of the 19 on board drowned, including Adeline Coquelin, the 12-year-old niece of Napoleon Bonaparte's divorced wife Josephine de Beauharnais. She is buried at St. Illtyds Church, Pembrey. The last large ship to be lost was the four masted windjammer, the SV Paul, carrying a cargo of timber and grounding in a storm in 1925. Today Cefn Sidan forms part of the Pembrey Country Park leisure and nature complex.
The beach is visually spectacular because of the fine structure of its sand granules – however, this makes it unsuitable for making stable structures beyond simple sand castles. On Sunday 3 August 2008 a 16-year-old boy was trapped when the tunnel he was digging in the sand dunes behind the beach collapsed. Swansea Coastguard said the alarm was raised around 19:10 BST, and a Burry Port coastguard team arrived within 15 minutes. After a helicopter air ambulance transfer to Morriston Hospital in Swansea, doctors pronounced him dead.
- Mary Curtis (1871). The antiquities of Langharne [sic] and Pendine. p. 12.
- "Landranger 159: Swansea & Gower". 1.25 inch map. Ordnance Survey.
- "Pembrey beach (Cefn Sidan)". Wales and Somerset Beach Guide. Retrieved 27 April 2016.
- Edmund Burke, 'Annual Register of World Events' Vol. 70, 1829, p. 266.
- "Wrecks on Cefn Sidan Sands". Carmarthen Bar and its shipwrecks. Retrieved 27 April 2016.
- "Beaches of Carmarthenshire". Discovering Carmarthenshire. Carmarthenshire County Council. Retrieved 27 April 2016.
- Mears, Tyler (20 July 2016). "The nudist beaches where people are really cooling off this summer". walesonline. Retrieved 2016-07-21.
- "Boy dies as sand tunnel collapses". BBC Wales. 3 August 2008. Retrieved 4 August 2008.