Kvernufoss is a hidden gem in South Iceland (actually not so hidden anymore), just minutes away from it's "big sibling", Skógafoss. It's around 30 meters high (98 feet) and cascades down moss-covered cliffs at the bottom of a small canyon. I highly recommend you make your way all the way behind the waterfall. This can be especially pretty on a sunny day as the spray from the water tends to create incredible rainbows. Since you do have to walk for around 20 minutes to get there, you will beat a lot of the crowds at Skógafoss and other easier-to-access attractions. The hike is relatively easy and definitely worth it!
QUICK NOTES:
What it is: A waterfall at the bottom of a small canyon
Best season: Any
Best time of day: Midday and early afternoon (this is the time when the sun is actually shining into the canyon)
Nice to know: You can walk all the way and get behind the waterfall - definitely worth getting a little wet for!