If you walk a bit further after Seljalandsfoss for about 10 minutes, you reach Gljúfrabúi, a beautiful waterfall hidden in a gorge/cave. You can walk inside the cave through a narrow valley and see how the water seems to fall out of the sky. But prepare yourself to be splashed wet by this mighty waterfall.

Tip: You can stay the night at the nearby campsite and visit the waterfalls before or after the crowds.