Graz' elegant palace was created for the Eggenberg dynasty in 1625 by Giovanni Pietro de Pomis (1565–1633) at the request of Johann Ulrich (1568–1634). Admission is via a highly worthwhile guided tour during which you learn about the idiosyncrasies of each room, the stories told by the frescoes and about the Eggenberg family itself.
Johann Ulrich rose from ordinariness to become governor of Inner Austria in 1625, at a time when Inner Austria was a powerful province that included Styria, Carinthia, and parts of Slovenia and northern Italy. His baroque palace was built on a Gothic predecessor (which explains an interesting Gothic chapel in one section of the palace, viewed from a glass cube) and has numerous features of the Italian Renaissance, such as the magnificent courtyard arcades.
The guided tour (available in English or German) takes you through the 24 Prunkräume (staterooms), which, like everything else in the palace and gardens, are based on astronomy, the zodiac, and classical or religious mythology. The tour either ends or starts at the Planet Hall, which is a riot of white stuccowork and baroque frescoes. The ticket for the tour (State Room Ticket) also allows you to visit the Schloss Eggenberg Museums and the rest of the 18 Joanneum museums within a 24-hour period from the time of purchase.