City Hall in Philadelphia. Built in celebration of the centennial it was considered a big, expensive mistake. (And it is still under construction over a hundred years later). It was actually built by a Scot in the late 1800s and meant to be the tallest building in the world…. Since it took 30 years to complete a number of buildings surpassed it’s eventual height (including the Eiffel Tower). It still is the tallest masonry building though (with 22′ thick walls to support the weight)!
In the 1950s, there was talk about actually tearing down City Hall for a new building built elsewhere. They found that the demolition would have bankrupted the city due to the building’s masonry construction. In 2006 it earned it’s place on the protected Historic Registrar.