The Reichstag is one of the coolest buildings in Berlin, which is saying a lot - there are a whole bunch of really freaking cool buildings in Berlin. So, the Reichstag is the building where the parliament sits. The parliament used to be called the Reichstag but is now called the Bundestag, and - bonus political note - if you call the parliament "Reichstag" now, it's a handy neo-nazi codeword. A little piece of nostalgia for the good ol' days of the Third Reich.
The Reichstag caught fire in 1933 and gave the Nazis an excuse to take away all kinds of freedoms.
Anyway. So it's a good old-fashioned German building, late 19th century, monumental, columns, all that good stuff. But on top it got this awesome glass dome, courtesy Norman Foster:
And it totally works! It's so cool! Dumbly, I have no picture of it from far away to show you, but trust me, it's totally cool to have this big shiny glass dome on top of the Reichstag. You can climb up inside on the spiral ramps:
Those mirrors reflect the sun down into the chamber where the parliament does its business - like the not-so-subtle symbolism? There's a great panoramic view from the top. I'm a fan.