Waterfall on Bildudalsvegur
This little waterfall is located right on the side of the road on your way to Bíldudalur from Reykjavik (coordinates 65.674109, -23.604694). It's on private land so you can only view the waterfall from the road either before or after you cross the little bridge but the waterfall is literally right beside the road so you're not too far away to begin with!