Below is a picture of the waterfall Svartifoss in the Skaftafell National Park, Iceland. A brief hike into the park and this wonderful waterfall appears in a valley out of nowhere. Similar formation can be seen at Fingal's Cave, Scotland and the Giant's causeway, Ireland. The basalt columns are formed by the contraction of hot rock as it is cooled, forming the amazingly geometric and regular shape.
I am currently studying volcanology in the UK and want to share this interest with others.