We spontaneously did this hike and were SO glad we did. It's the second tallest waterfall in Iceland and offered some amazing views! We really didn't know what we were getting into, but we had read about it the day before, and decided to do it. It's pretty steep with some fun ropes and a fun river crossing. The views were amazing at the top, it definitely surpassed all expectations. Please note that the bridge to cross the lower river and hike to the eastern side is only open from May to October.

PHOTO TIP: The best spots for photos are not the viewpoints at the top, rather about halfway up where you can get amazing views of the waterfall.

https://www.alltrails.com/trail/iceland/capital/glymur-waterfall-trail?u=i