Belvedere Palace was originally built in Baroque style by Prince Eugene of Savoy. The Palace consists of two sections, an upper section built between 1720 and 1723 and a lower section constructed as a garden villa in 1716. The two sections of Belvedere Palace are connected by a garden, but, as you can see from the second photo, it was being reconstructed when I was in Vienna.
The original Belvedere and grounds were sold to Maria Theresa in 1752 and, under the Habsburgs, the Palace was expanded.
Belvedere has undergone extensive restoration three times since WW II - first, right after the war, again from 1988-1996, and a final time that began in the early 2000s and is not yet completed.
Belvedere Palace houses three museums: the Museum of Medieval Art, the Austrian Baroque Museum and a Gallery of 19th and 20th Century Austrian Art.