The closest is Palais Equitable, 1 km south-west of the city centre; the most famous is Schönbrunn Palace (#17 of 9,035 worldwide) 5 km south-west. The oldest dated site in the circle is Carnuntum, founded 50.
The 100 km circle reaches into 4 countries: Austria (94), Slovakia (29), Czech Republic (11), Hungary (6).