Expect some fog and even some rainy days if you visit Vienna in autumn, but it won't be enough to put a damper on your stay in contrast with the mild weather and sunshine you can enjoy the rest of the time. Plus, with the wine harvest in full swing you're sure to find plenty to do and little to complain about. Reserve a car hire in Vienna to enjoy the autumn weather during your vacation.
The hills just north of Vienna are filled with vineyards and the hiking there will be colorful and nice by October. For an excellent little daytrip take your Vienna car rental out to Baden and hike through the vineyards to Kumpoldskirchen, where you can visit several Heurige taverns.
Held in late October, Viennale is a film festival of more artsy or independent films. Perhaps you're a dedicated independent film fan, in which case this festival will surely delight you, and for everyone else it can be an entertaining way to spend a rainy fall day.
October is the last month before the biting cold of winter, and late enough to miss the crowds of summer - perfect for enjoying the hills of the local parks and the view of the city from Kahlenberg. Head over to the parks of Schloss Schönbrunn in your Vienna car rental, and feel like the park is yours without the huge droves of summer tourists.