Well, more precisely: it should have become one but never actually was completed. On the contrary, Empress Maria Theresia of Austria cannibalised Schloss Neugebäude and used parts of the (incomplete) castle for her new big representative castle, the famous Schloss Schönbrunn.
Schloss Neugebäude, however, was not used up completely for Schönbrunn. It was only a few years ago that the castle was 'rediscovered', so to speak, and is now being restored. This is the west tower of Schloss Neugebäude:
In summer, the castle now is regularly used for smaller events and open air cinema. It still looks a little bit more like a restored ruin than a magnificent castle, but maybe that will change in the years to come.
