Berlin’s Reichstag dates from the late 19th century, although its function as a seat of parliament ended in 1933 with the rise of the Nazis, and a fire which gutted the building and served as a pretext for the suspension of civil liberties. The building retained its symbolic power as demonstrated by the famous photo of a soldier planting the Soviet flag on its roof at the end of World War II (and you can still see Russian graffiti left by his comrades).
Long-term Berlin residents generally date the start of the city’s tourism boom from the time that artist Christo famously wrapped the building in 1995. Four years later it reopened as the seat of the German Bundestag (equivalent to the House of Representatives) for the reunified nation. By then the building had been completely redesigned by British architect Norman Foster, who gave it a new glass dome, a symbol of political transparency.
Visiting the Reichstag roof is free, and until recently you could just turn up and join the (often lengthy) line for the elevators. However security concerns mean that you must now register beforehand. You can either sign up in person at the ticket office (in front of the Reichstag, to the right if you’re facing the building), or online.
Once on the roof you have Berlin laid out before you, from the green expanse of Tiergarten to the soaring spire of the TV Tower. You can visit up to 11pm to see the city light up, particularly the buildings of nearby Potsdamer Platz. Alternatively, to skip the line book a table at the rooftop Käfer restaurant, served by a separate entrance; before or after your meal you’re free to stroll the roof.