Svartifoss (Black Falls) waterfall

Svartifoss (Black Falls) is a waterfall in Skaftafell National Park in Iceland, and is one of the most popular sights in the park. It is surrounded by dark lava columns, which give rise to its name. The hexagonal columns were formed inside a lava flow which cooled extremely slowly, giving rise to crystallization. Similar well-known lava formations are seen at the Giant's Causeway in Northern Ireland, and on the island of Staffa in Scotland. These basalt columns have provided inspiration for Icelandic architects, most visibly in the Hallgrímskirkja church in Reykjavík, and also the National Theatre.
From tommyimages.com