There are quite a few black sand beaches in Hawaii, but this was by far the most beautiful, it was also empty from the crowds.
We found this beach near Sandwich in Cape Cod. We took a small walk in the sand, almost alone, not many people, it was high tide. Went to lunch and when we came back to pick up the car. What a surprise! Lots of people gathered now in the beach, playing games, walking the beach, walking as far as we could see (dark dots on the horizon, if you care), it was low tide.