In the 50's, the Soviets were prospecting for natural gas in Turkmenistan, and accidentally lit this 60m-diameter crater on fire. It's been burning ever since.
Self promoting this video back to the front page; last published Wednesday, March 26th, 2008 4:44pm PDT - promote requested by original submitter arvana.
edit: Sorry, instead of via I should have said "see also".
http://www.reddit.com/info/6ogp0/comments/
I knew the Russians did it.