Giants Causeway is a great natural wonder and one of Northern Ireland's most noted landmarks. Formed by a volcanic eruption 50 - 60 million years ago, this UNESCO World Heritage Site is a mass of tightly packed pillars that jut out from the sea. The Causeway Stones, as the volcanic rocks are known, are polygonal columns of quickly cooled lava called columnar basalt. Their large number, 40,000 or so, has inspired legends of sea striding giants. Their odd shapes have stirred funky names such as Chimney Stacks, Wishing Well, Giant's Boot, Camel's Hump and Lady's Fan. Their unique geology has greatly contributed to earth sciences. Their dangerous nature has grounded at least one ship. The Girona, a Spanish Armada, ran ashore here in 1588.