I thought I would share some ideas on where to get great views (many for free) of Vienna. Happy exploring!
Upper Belvedere - It makes sense that the Belvedere (literally a building with a view) has a great position over Vienna. The gardens of the Belvedere are free. The palace is divided into an Upper and Lower Belvedere, each are art museums with the Upper housing the family Kiss by Gustav Klimt. Between the palaces is a historic garden with fountains, flowers and hedges (and joggers). The Upper Belvedere offers a sweeping view of the city and the Kahlenberg. The garden can be accessed from Trams D and 71 or by foot from the center in about 15 minutes.
Kahlenberg - This "mountain" lies at the edge of the city in the 19th district, famous for vineyards and heurigen. The views on a clear day are spectacular. Keen eyes can spot the Prater's Ferris Wheel, Belvedere Palace, the Spittelau incinerator and St. Stephan's. To reach the view, which is free, take the 38a bus to Kahlenberg from the end station of the U4 subway line at Heiligenstadt. Exit the bus in the large parking lot (not the Cobenzl stop!) and walk towards the church. Next to the church is a terrace where you can take it all in, especially the re-engineered Danube River and the recreational Danube Island. You can then take the bus back down (boring) or follow Stadtwanderweg 1 signs (back towards the parking lot) which will take you to Nussdorf where you can hop on a tram back to the city center. Along Stadtwanderweg 1, you will walk through a gorgeous forest, vineyards and continue to have amazing views of Vienna. Stop at Mayer am Nussberg for a glass of wine or grape juice. When you reach Nussdorf, have dinner at my favorite heuriger Schuebel-Auer.
Lainzer Tiergarten Wienerblick - This expansive park was once royal hunting grounds on the edge of Vienna. Hermesvilla, a small palace Franz Joseph built for his wife Sisi, in the middle of the area can be visited to free the first Sunday of every month. Most of the area is forested and there are well-marked trails and several huts serving food. A hugely popular area is the field surrounding the Wienerblick (Vienna view). Wild boars and deer also freely roam this area, which is particularly beautiful in the fall. I suggest using Google maps to determine the best way to reach the main entrance to this park, Lainzer Tor.
IKEA at Westbahnhof - The urban IKEA, a new concept started in Vienna, located at Westhabnhof has free amazing views of Vienna, particularly Mariahilferstrasse, on the roof. Elevators at the entrance will take you straight to the top, where you will also find a bar and an IKEA restaurant. A great place to chill and get some cheap food.
Haus des Meeres - The aquarium in Vienna is located inside of a WW2 anti-aircraft bunker that is too thick to be removed. The top of this massive building has a 360 degree terrace which can be accessed for free. As the top is quite central, you can spot some really interesting rooftop apartments as well as most of the major buildings in the city.
MQ Libelle - This newly opened rooftop terrace is free on top of the Leopold Museum. There is also a bar. I haven't been here yet, but I hear good things. Let me know!
Jubiläumswarte - This one is not for the fainthearted. First, to access this spiral staircase tower on top of a mountain overlooking Vienna, you have to walk. I suggest following Stadtwanderweg 4 - look at this link for the map and more details - https://www.wien.gv.at/umwelt/wald/freizeit/wandern/wege/wanderweg4.html. To access the start of this trail, take tram 49 (starts on the Ring) to Rettichgasse. Then just follow the signs. I was last here on a gorgeous fall day and the colors of the wood on wood side was as beautiful as the view of the city on the other side. Well worth the effort.
cont'd below