The inscription "DEM DEUTSCHEN VOLKE" on the facade translates to "To the German people".
The Reichstag building, designed by Paul Wallot, was finished in 1894 and originally featured a heavy, traditional stone and iron cupola.
The original dome was severely damaged during the famous Reichstag fire of 1933 and further ruined by Allied bombing campaigns in World War II. The remnants of the original dome were completely demolished in the mid-20th century.
Following German reunification, British architect Sir Norman Foster led a massive renovation of the building. The current high-tech glass dome was completed in 1999 (specifically 105 years after the building's initial completion).
The dome was intentionally designed to be transparent, symbolizing a new era of open, public-facing German democracy.
The glass dome is a very popular tourist attraction. In this photo, you can see tourists near the glass wall, admiring the view of Berlin.
I didn't go up because, at the time, you had to book two to three months in advance.