Our time in Iceland is limited so we're not sure we want to take the time to drive to Diamond Beach. We're doing the Golden Circle and could head east from Selfoss, but we're concerned about the time spent driving there as a dead-end. What about the other black sand beaches along the south coast? How do they compare? Thanks for your suggestions and impressions.
I have only been to Reynisfjara beach near Vik, on a guided day tour. It was a very cold, windy, and rainy day in late October, but still a spectacular sight. That particular beach has very dangerous sneaker waves so you do need to watch out. There are quite a few places to stop along the way from Golden Circle. It is a big long drive for sure, so understandable you might want to make other choices about your time.
You will see more than black sand beaches on the south coast. If time is limited, don't worry about trying to get to Diamond Beach. You'll see other beaches and glaciers and gorgeous scenery. We made a lot of unplanned stops.
You do not want to miss this one. The others just are not the same. Hard to describe, but Reynisfjara with the cliffs etc is just beautiful. As mentioned, you need to be very careful there though due to sneaker waves. They now have a warning system in place there with lights to let you know what level of danger it is at any moment, but you still want to use common sense. No turning your back to the ocean, do not go inside the cave at the cliffs, etc.
Diamond Beach is lovely, but really not worth the trek by itself. The glacier across the road is worth the long drive out along with Diamond Beach, however. It is not as vast or wild as Reynisfjara. Diamond Beach will have ice (diamonds) in black sand, while Reynisfjara will not.
If your time is limited, stick to Reynisfjara near the lovely little town of Vik (which itself is worth a short visit and stop for lunch). Doing this will save you quite a bit of drive time.