If you think the city hall in Copenhagen is big and impressive, then you should take a look at the main city hall in Paris. Little wonderful Denmark can't really compare any longer. The building is almost a small palace, with towers, chimneys and interesting details which are so typical for the renaissance buildings of Paris.
As so many buildings in Paris, Hôtel de Ville also has a lively history. The building were finished in 1628, nearly a century after the first plans were made. It was built as a city hall for Paris and still functions as such. The place was stage for many important historical events, especially during the French revolution.
The city hall was expanded in 1835, where two wings were added to the main building. In 1871 the place was burnt to the ground, only leaving the outer walls. The fire also destroyed most of the public documents from the period around the French revolution.
A couple of years later the rebuilding was started. It lasted almost 20 years. Today the facade stands as it did in the 16th century, while the interior has a style from the 1880's.
It is quite the fascinating history and life the city hall has lead, I wish the building itself could tell the stories. I'm sure that would produce many thick and interesting books for months of reading.
Metro: Line 1 and 11, stop Hôtel de Ville