Schloss Eggenberg like many a palatial dwelling it had antecedents as a real castle. But then it was developed from the bottom up as a palace. I'm going to write in here verbatim the description from the brochure we received.
The house is named after the man who had it built - Prince Hans Ulrich von Eggenberg (1568-1634). Work started on the showpiece building in 1625. By then, the prince was already a key figure at the imperial court in Vienna. As a close confidant of Emperor Ferdinand II, he steered the political fortunes of the empire through the early days of the Thirty Years' War.
Eggenberg Palace is an expression of his position of power, and at the same time a symbolic representation of his humanist values. The architecture is programmatic, following a scheme worked out in minute detail. It was conceived as a portrayal of the universe, imbued with philosophical ideas of cosmic harmony. the calendar and mechanisms of the heavens, earthly hierarchies, world history, religious concepts and values were incorporated into the scheme, as were alchemistic and astrological notions about the construction of the universe.
You can only see the inside of the UNESCO Heritage Monument by guided tour. There was so much detail presented it was hard to remember it all. Basically the palace is in as close as possible to its state from the 18th century. It has never been updated with electricity or heating. So with that let's go visit.
So let's take a look shall we.
(Keep in mind that there are literally hundreds of room that were decorated thus!)
And from the museum (over 500 paintings!) an example of the real color of Gothic period stained glass.