Stuðlagil Canyon is one of our favourite spots and hikes. It is about 7km return from the car park. You can reach a main viewing area at one parking lot, but if you can I would recommend doing the hike to see the river from below. The 2 car parks are at seperate spots near each other, so make sure to check googlemaps.
!hile getting down to river level takes a steeper, uneven path that needs good footwear and some caution near the edges. Visit in late spring to summer when glacial melt makes the water most vivid, aim for early morning or evening to avoid crowds and harsh light, and be prepared with layers, sturdy shoes, water, and insect repellent; there are no real facilities on site and parking can fill up on busy days.