Hengifoss is an impressive 128-metre tall waterfall in East Iceland making it the third biggest waterfall in Iceland. You start by hiking along either side of a ravine leading towards the bigger canyon. When you reach it, you can either hike up and along the edge of the canyon (careful!) or into the actual canyon (recommended). Both are awesome but for the most immersive experience I'd say hiking into the canyon is the way to go. Recently a bridge was built, at the entrance of the canyon, so you can actually hike up one side of the ravine and back down the other side. The hike takes about two hours (round trip) from the parking lot (around 2.5km / 1.5 miles each way).
QUICK NOTES:
What it is: Probably the most famous waterfall in East Iceland.
Best season: Late spring or summer (for the most power in the waterfall).
Best time of day: Midday (in the summertime, during sunrise and sunset, the sun will shine from behind the waterfall and be too low to reach the bottom of the canyon).
Nice to know: You can either walk along the canyon or into the canyon itself. I have done both and honestly can't tell you which one I prefer but for the most immersive experience I would probably hike into the canyon and get as close to the waterfall as I could. There is a bridge over the ravine (leading up to the canyon) so you'll be able to hike up one way towards the canyon/waterfall, go over the bridge and back down the other way.