Much has been lost in the name of progress, however a few great losses immediately come to mind.
Penn Station was completed in 1910 and was considered a Beaux-Art style masterpiece and an architectural jewel of New York, however in 1964 it was demolished. The station was the largest public space in the world and was based upon Doric designs from Milan and Naples. The reasoning behind its destruction was related to declining passenger numbers and the value of the station for redevelopment. A new smaller underground station was built following its destruction however it was nothing in comparison to the original station.
At around the same time in the United Kingdom as passenger numbers increased, another great architectural masterpiece was being destroyed. Built in 1837 Euston Station was one of London’s first major stations, however 1962 the station was considered to small so was rebuilt. The old station claimed to have the largest Doric propylaeum ever built. When expanded in 1849 the architectural sculptor John Thomas contributed eight allegorical statues representing the cities served by the line. The new station had 18 platforms and now serves 38 million passengers annually.