Urriðafoss is a waterfall in Þjórsá River. Þjórsá is Iceland’s longest river, 230 km. This mighty river drops down, 360 m3/sec by the edge of Þjórsárhraun Lava Field, in beautiful and serene surroundings. Þjórsárhraun lava field is the result of the greatest lava flow on earth since the Ice Age. Located right off Ring Road 1.