The finest (and only) black sand beach that I've ever been to.  It was really cool!  In both senses it was too cold to go swiming in, but the sand was cool to look at.  Something about lava hitting the water and exploding or some other weird science...whatever, don't care, it's the beach!
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/63122283@N06">Nelo Hotsuma</a> from Rockwall
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/63122283@N06/24482910355/">Punalu'u Beach</a>