By far the most visited place in Vienna is the Schoenbrunn Palace which housed the Habsburg famiiy as a summer location. Originally on the outskirts, it is firmly in the city now and it is spectacular. Find a history of the Habsburg’s here as they were the most successful imperial family since the Roman Empire: <https://www.britannica.com/summary/House-of-Habsburg>.
Some photos of the grounds of Schoenbrunn Palace
The Habsburg’s also maintained an Imperial Palace in downtown Vienna and it is not only huge, but houses the famouus Spanish Riding Academy. <https://www.wien.info/en/art-culture/imperial-sights/imperial-palace-348842>.
The stables for the Spanish Academy horses and one being taken out for training. For more here is the website: <https://www.srs.at/en/>