The maar Víti and Öskjuvatn caldera lake in Iceland
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/25588248@N00">Jon Connell</a> from Cambridge, UK
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/25588248@N00/228271653/">Öskjuvatn</a>