The BBC has a good write up about it here.
"Some 80 million trees were flattened over an area of 2,000 square km (800 square miles) near the Tunguska River. The blast was 1,000 times more powerful than the atomic bombs dropped on Hiroshima and Nagasaki and generated a shock wave that knocked people to the ground 60km from the epicentre."It took 13 years before any outsider is known to have actually visited the site, and another six years for a formal expedition to arrive (remember in 1927 the Soviet government had far more pressing things to do oppressing the masses and changing them into Lenin's new men).
As the article says, had it hit central London, the entire metropolitan area of Greater London would have been razed clear as far out roughly as the M25. It's a reminder that Earth is vulnerable to the flotsam and jetsam of the universe entering its atmosphere. Almost all of that burns up. Here is hoping that those watching the sky can warn us all sufficiently in advance and allow action to be taken - after all, a large object striking the oceans would be far more catastrophic than another one at Tunguska.Of course there is also much interesting reading on the wiki post.