Tunguska

CNN has an article on a re-evaluation of the Tunguska event - an enormous explosion in a remote part of Siberia in 1908 that is variously attributed to an asteroid or comet impact. The Wikipedia article discusses the history, which is pretty interesting - what with world events and the remoteness of the location it wasn't till 1927 that anyone went to the spot of what is almost certainly the largest impact to have hit the Earth in recent times.