Barton Creek Cave (or possibly Footprint Cave), Belize
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/49580580@N02">Thomas Shahan</a>
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/49580580@N02/10078599093/">Barton Creek Cave</a>