The Archbishops of Cologne had a double function as Electors in the Holy Roman Empire and as a result tended to be powerful people in Europe. In the 1600s and 1700s such people tended to build big palaces to impress their subjects, to impress other leaders and to serve their own vanity. Once Louis XIV built Versailles, princes and archbishops everywhere in Europe had to copy this fad, on a smaller scale of course. Most had winter palaces and summer palaces, and the Archbishop of Cologne had a summer palace in Bonn. Is it Versailles? No, but its the best such Baroque Palace that you can find in the Rhineland. As for parking, hahahahahahahaha. Parking is not very car friendly. GO early or go late, during the middle of day you will have to have a lot of patience and some luck. There can be spaces along the Poppelsdorder Allee which connects the university with the palace. But you will need some luck. There is a large lot (paid) at the train station but its somewhat of a hike to the palace. If you visit when the university is not in session, things are easier. There are not many underground parking garages in the Altstadt and they are expensive and small. Most of the side streets in residential neighborhoods have severe restrictions. Good luck. This palace is not Versailles, it does not get millions of visitors per year so there is not much parking infrastructure.