From
World Heritage Convention site :
The site lies on the north coast of the County of Antrim, Northern Ireland, and includes the Causeway Coast extending for about 6 km between Causeway Head and Benbane Head. The Causeway Coast has an unparalleled display of geological formations representing volcanic activity during the early Tertiary period some 50-60 million years ago. The most characteristic and unique feature of the site is the exposure of a large number of regular polygonal columns of basalt in perfect horizontal sections forming a pavement.
Tertiary lavas of the Antrim Plateau, covering some 3,800 km2, represent the largest remaining lava plateau in Europe. The coastline is composed of a series of bays and headlands consisting of resistant lavas.
The average height of the cliffs is 100 m, and has a stepped appearance due to the succession of five or six lava flows through geological time. This geological succession during the Tertiary period consists of the Lower Basalts, where about six of the 11 lava flows are 67 m thick and are exposed between Plaiskin Head and Benbane Head; the Interbasaltic Bed which are exposed along extensive sections of the cliffs east of Giant's Causeway; and the Middle Basalts, which are thick flows ranging from 30 m to over 150 m. The Giant's Causeway displays the columnar basalt structures and includes the Specific sites of interest include the Giant's Causeway itself (a sea-level promontory of almost entirely regular polygonal columns averaging 45 cm in diameter and numbering 40,000 columns), the Giant's Organ (60, 12 m high regular columns and the three-tier structured Middle Basalt), Chimney Tops and Hamilton's Seat (a viewpoint). The coastline is also cut through by olivine and theoleiite dykes.
In addition to its geological features the site has a range of habitats covering seashore, cliff, scree, grassland, scrub, heathland and marsh.
The Giant's Causeway itself (a sea-level promontory of almost entirely regular polygonal columns averaging 45 cm in diameter and numbering approximately 40,000 columns); the Giant's Organ (about 60 regular columns, 12 m high; Chimney Tops (a number of columns separated from the cliffs by erosion); and Hamilton's Seat (a view point). The coastline is also cut through by olivine and tholeiite dykes, a good example of which can be seen at Roveran Valley Head. Exposure of these columns, in perfect horizontal sections at such a scale creating a pavement, is considered a unique combination of features.
The wreck site of the Armada gallesass Gerona in Port-na-Spaniagh, below the isolated columns known as the 'Chimneys', is of considerable cultural importance. The sublittoral area is a protected nautical archaeological site, and the treasures and other Armada artefacts recovered by Robert Stenuit and his team between 1967 and 1969 are conserved in the Ulster Museum, Belfast. This collection is a major part of all known recovered Armada artifacts.
The Giant's Causeway featured in the 18th-century geological controversies on the origins of basalts. There is an interesting cultural heritage associated with place names, and other local history such as the kelp (seaweed) and fisheries exploitation carried out by local communities, documented mainly in the 18th to mid-20th centuries.
Note: Free entrance, but you have to pay the car parking (about 8-10€)