Most of our time in Iceland was like living in a Tolkien novel. Weaving through the ravine that is Ásbyrgi was surreal. Large plateaus on either side of us walking through brush and shrubbery. Hiked up the side of one to get a better view, requiring us to scale a wet rock face with the assistance of a rock. Safety first.
While we were not able to visit Dettifoss during our time in Iceland, we did manage trips to both Goðafoss and Gullfoss. We hiked around the top of Goðafoss, peeked over the edge, jumped around rocks, normal safe stuff. Gullfoss included icy rocks and pebbles, no rainbow, but a pretty great view of a massive waterfall.