There are three altitude locations that you can see Vienna with a bird-eye view. They are Cobenzl, Kahlenberg and Leopoldberg. All of them are lined along with a sole Wiener Linien Bus number 38A Line. Even if they are located outside Vienna, but you can arrive there by a Wiener Linien Bus without extra charge.
From the U4 Heilingenstadt station, you can take the Bus No. 38A up the hill with both side views of beautiful houses and buildings. The bus will further lead you to a nice view of forest, leaving a residential area behind. Some parts of the road were made of classic cobble stones; however, the majority of them has been replaced with asphalt and cement material. A first view point you can stop is Cobenzl. There are restaurants and coffee shops which you can have lunch or dinner or can sip a cup of coffee and leisurely view a vineyard (Weinberg) below your horizon. Then, taking the same 38A bus furthers up the mountain to Kahlenberg. Upon arrival at Kahlenberg, you will see a hiking track which can lead you by foot or by bike to Vienna. Behind a popular view point of Kahlenberg stands a holy church namely Sobieski. It was honor after a name of the late Sobiesky King of Poland, who set Vienna free from the Ottoman Empire invasion.
Walking towards a broad terrace of Kahlenberg, a beautiful panorama of Vienna is in front of your sight. Many tourist attractions can be viewed as Saint Stephen Cathedral, Rathaus, Vienna International Center, Donau Park, Danube Tower, Danube River, New Danube river, Old Danube river and etc. On a nice weather day, you can even see a plane taking off or landing at the Vienna International Airport.
After fulfilling yourself with a beautiful panorama view from Kahlenberg, please do not rush back to Vienna. You may consider take the same Bus line to Leopoldberg. At Leopoldberg, you will enjoy a better view of the merging two lines of new and old Danube rivers. I went there at least three times and have never gotten bored of walking along the stairs surrounding the Leopoldberg Church while viewing the Danube in different angles.