Fifty shades of green: the Gullfoss waterfall.
One of Iceland's most famous waterfalls is the Gullfoss waterfall. This waterfall can be found in the Golden Circle, the most famous and visited area in the whole of Iceland. That makes it the busiest. Well, don't think about the masses of tourists you'll encounter in Amsterdam or Haarlem, more of a village in Friesland.
The Gullfoss waterfall is located in a river: the Hvítá (white river). The water in the river comes from the glaciers, mixed with rainwater. You'll find the Gullfoss at road number 35, about ten kilometres from the famous Geysir, the geyser that spits meters high every few minutes.
I have had the pleasure of visiting the waterfall in summer and winter. Both times I was impressed by the thundering violence that plunged thousands of gallons of water per second. The beauty of visiting in summer is that the continuously splashing water, which forms a mist, often shows rainbows at the waterfall. You can also go for a nice walk and get closer to the waterfall. However: Stay behind the ropes! The area around the waterfall is fragile, and if you slip, they'll never find you back.
When you drive to the Gullfoss (this is excellent), so you pass the Geysir. This world-famous Geyser sprays meters high, and is a five-minute walk from the road. You walk along a landscaped, even path, and see multiple hot spots. For my taste this area is too much laid out, and it was very busy, I didn't take pictures of it, also because it was raining quite a bit when I was there.
Back to Gullfoss: On arrival you can park your car in a large, free, car park. At the time of writing, a toilet block is being built, where you have to pay to use it. My tip: walk inside the visitor center, with shop and restaurant. In the back you will find rows of free and well-groomed toilets. Of course I don't know how long these are still available.