Svartifoss (Black Fall) 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 gave rise to its name. Other well-known columnar jointing formations are seen at the Giant's Causeway in Northern Ireland, Devil's Tower in Wyoming, USA and on the island of Staffa in Scotland.
The base of this waterfall is noteworthy for its sharp rocks. New hexagonal column sections break off faster than the falling water wears down the edges.
These basalt columns have provided inspiration for Icelandic architects, most visibly in the Hallgrímskirkja church in Reykjavík, and also the National Theatre.
Source : wikipedia