A huge fireball, the roar of which fills your ears - and a whole city is levelled to the ground. Thousands of people have been killed, millions injured, and the economic damage is approaching billions of dollars. This is how the Tsar Bomba works - the most powerful thermonuclear bomb ever invented. But what if a million such bombs exploded in the deepest point in the Earth's surface - the Challenger Deep? It's all much more terrible than you can imagine.