On the fifth of November the British (and some of their former colonies – apparently they still celebrate in New Zealand) commemorate the Gunpowder Plot of 1605.
On 5 November 1605 a group of Catholic conspirators, including the most famous member of the group – Guy Fawkes – tried to blow up the Houses of Parliament in London. The idea was to assassinate King James I and various Protestant members of Parliament during the opening ceremony. Fortunately for the King, but less fortunately for the conspirators, the plan was discovered and the plotters were executed.

The great explosion having been avoided, the British use it as an excuse for annual parties, lighting bonfires (the night of 5 November is called Bonfire Night) and burning effigies of the plotters (the straw and fabric figures known as “Guys”, named after the most famous of the conspirators) and firework displays.

If you’re interested in finding out more about this British custom: http://en.wikipedia.org/wiki/Gunpowder_Plot
Or, for something a bit more fun, a video explaining the history of the events: