~Philadelphia City Hall, Philadelphia PA

One of the largest municipal buildings ever built. It had a mixed reception upon completion, with detractors calling it "the marble elephant". People warmed up to it though, and it is now one of the city's most famous landmarks.

Largest municipal building in the United States, with over 700 rooms.
It was the tallest habitable building in the world until 1908, and remained the tallest in Pennsylvania until 1932.
A gentleman's agreement stipulated no building in Philadelphia was supposed to be built taller than it. This agreement lasted until 1986.
The building is built from solid granite and brick, with walls up to 22 feet thick.
City Hall was nearly torn down in the 1950's, but investigators found that demolition would literally bankrupt the city.