The fall of the Berlin Wall, of course! 

But how many people know why it was there, what it meant for the people trapped by it, what the world behind the wall was like and why it fell?

Not enough, in my opinion. Although you'd have probably brushed on it if you took GCSE History (I wish I did), there is a shortage of education on this subject, and not just in schools. I say self-educate, and keep in mind the fact that this affair was very recent and how those who lived under the rule of the GDR/DDR before continue to be affected by that time.

I strongly recommend reading "Stasiland", by Anna Funder. It's an amazing book. Try to get an old copy if you can. I hear that, somewhat ironically, former Stasi people forced her to edit it in the later editions.

For people on my course, I'll lend you a movie called "The Lives of Others", if you ask nicely. Just remember that, while it's a cinematic masterpiece, it's fiction and no Stasi agent could have done what Wiesler did in the movie!

For now, read this excellent article from The Times.