At Litlanesfoss, the waterfall cross-sections an ancient lava flow, which formed columns as it cooled. http://photography.nationalgeographic.com/photography/photo-of-the-day/litlanesfoss-waterfall-iceland/
The famed Cliffs of Moher in County Clare. It's awesome and scary, almost hypnotic. These friendly sheep were grazing along the edge when I was there. The edge has no safety barrier, so watch your step, it's a long way down.