The Giant's Causeway is a cool spot in Northern Ireland with about 40,000 hexagonal basalt columns that look like stepping stones leading into the sea. Legend has it that a giant built this causeway to fight another giant across the water. Tourists have been checking out this natural wonder since the 19th century, and now there's a visitor center where you can learn more about the site's geology and history. It's a popular place to visit, attracting nearly a million visitors each year.