If you want to have a memory that most visitors to Vienna haven't experienced, take bus 38A up to Kahlenberg. Here you get an amazing view of the entire city, Danube and surrounding Vienna Woods. If you arrive near dusk, you can see where you are going as there aren't any lights around the site. We always travel with a flashlight, so you might find that useful. At night, the lights of the city spread before you. Nearby Josefsdorf also provides a good view. The bus can be reached by taking tram 38 to Grinzing and then bus 38A up the hill. This site also has historical significance as both Turkish troops and Napoleon fought battles here.