Gljúfrabúi, the hidden waterfall, lies at the foot of Eyjafjallajökull volcano and is part of Katla Geopark. It is just 600m from much better known Seljalandsfoss and much less crowded. To get to the waterfall you either have to wade the stream or balance on wet rocks and once you are in front of the falls you get a full shower - I stayed outside;-)

See note for context.