BASTILLE

The French Revolution began when the people of Paris stormed the Bastille on July 14, 1789. Yes, that's the date France celebrates as the start of the Revolution. And, if you're to pick a specific date for something as complex and incremental as the start of the Revolution, it may be as good a date as any. But by that date, lots of other things had happened - the convocation of the Estates-General, the Tennis Court Oath, the meeting of the National Assembly - that probably would have propelled the Revolution forward if the Bastille had never fallen.
To put it another way: the cork was coming off the bottle and it probably would have popped with or without the fall of the Bastille.
Above all, the storming of the Bastille made a great symbol. Also, it's more fun to set off fireworks for an event that involved actual cannon fire and bloodshed than for something as civilized - but central - as a bunch of middle class men in frockcoats standing around a tennis court (actually, a badminton court).
For more see (in English) The Origins of the French Revolution and Liberty, Equality, Fraternity: Exploring the French Revolution or (in French) La Révolution Française: 1789-1799

The people who stormed the Bastille wanted to free the prisoners. They wanted to get their hands on weapons and gun powder which had been stored there. In fact, they FORGOT to free the prisoners before taking the keys of the cells out to parade them through the streets. Oops.

The Bastille held numerous prisoners when it fell. It held seven prisoners when it fell. After the period of its greatest use (under Louis XIV), it had held far less prisoners under each succeeding regime.

Most of its prisoners were innocent victims of arbitrary power. These did exist, over several hundred years. But most of the people in it had committed crimes, at least by the laws of the time, and often by modern laws as well (fraud, forgery, poisoning, etc.)

The Bastille was the worst prison in France. Not by a long shot. In fact, since it often held aristocrats and other people with powerful friends, it may have been the best prison in France - if only by default. (French eighteenth-century prisons weren't great fun in general.)

It was the last bastion of arbitrary tyranny. After the Bastille fell, France had lots of prisons left - including, near Paris, another so-called 'Prison of State', Vincennes (which still stands today). Diderot, Mirabeau and de Sade had all spent time there. France's remaining prisons got plenty of use during the Revolution, which could be pretty arbitrary itself.

The Paris mob tore it down. The Bastille was torn down as any big building would be today - by a paid demolition crew. In fairness, though, the man who got the contract for the job was known as 'Patriot Payot' and seemed to regard his mission as something more than a profit-making venture.

This was the first time it fell. The castle had been taken over at least four times, twice by or on behalf of the people of Paris:

• On June 11, 1418, as the Burgundians invaded Paris, the people of Paris besieged the castle and, (as in 1789) when the occupants surrendered under a guarantee of safety, massacred many of them anyway.

• In February 1565, the Prince of Condé briefly entered the castle, despite the refusal of the Marshal of Montmorency.

• On November 15, 1591, during the troubles of the League, the castle was surrendered to the forces of the Duke of Mayenne. It was returned to Royal hands on March 22, 1594, when Du Bourg, who had been given command of the castle, capitulated to the Marshal of Matignon.

• On January 17, 1649, during the troubles known as the Fronde, the Bastille surrendered to the people of Paris, though in a far more orderly fashion than in 1789. Two representatives of Parliament were sent to demand its surrender. When the governor refused, forces of the Prince of Condé briefly besieged it and he surrendered. Command of the castle was given to a person chosen by the people of Paris.
  On July 2, 1652, in a famous incident, the Great Mademoiselle - grand-daughter of Henri IV and a cousin of the young Louis XIV - directed cannon fire from the Bastille against Royal forces. At that point, there had still been some question of marrying her to the King, but, it was said at the time, "with this cannon shot, she killed her husband".
  The castle was not returned to Royal authority until October 21, 1652.

Only the people - and enlightened intellectuals - wanted it gone. The idea of tearing down the Bastille had been kicked around for a while in official circles, through for financial, not humanitarian reasons - it cost far more to run than other prisons and rarely held many prisoners.