This is a little secret not many tourists know about. It's very close to Seljalandsfoss but far less crowded.
The waterfall is at the end of the canyon and it requires a bit of climbing to get there. One passage you need to climb along a rock wall holding onto chains. It's not the easiest hike but well worth the reward at the end when you see the waterfall.
You'll definitely get wet so bring your waterproof gear.