I love it when the world does my work for me! Have you seen the story about the sinkhole in Guatemala? http://news.nationalgeographic.com/news/2010/06/100601-sinkhole-in-guatemala-2010-world-science/
It is an amazing 30 stories deep and looks nearly perfect in its circular shape. As a matter of fact, it is so big they aren’t sure how to fill it! Or even if they can!
Take a look at this and tell me you aren’t inspired to write something to explain how it came to be…I dare ya! 🙂