Vienna

1. The Prater: the entire public park, not just the amusement park
2. Hundertwasser House
3. Stroll the Ringstrasse
4. Kunsthistorisches Museum (literally Art History Museum)
5. Visit a heuriger (wine tavern associated with a vineyard)
6. Visit the natural history museum
7. Stefanskirche, even if you only enjoy its spectacular exterior

My recent trip report might give you some ideas.

https://community.ricksteves.com/travel-forum/trip-reports/sisters-in-vienna-and-prague-our-trip-report

Have a great trip!!

https://community.ricksteves.com/travel-forum/austria/a-few-days-in-vienna#2474986

Last summer. I visited the famous Sacher Hotel - reserved a table for Bel Etage Cafe. I got a window table. Nice. I like the famous Cake „Sacher Torte“ and Meal „Wiener Schnitzel“.

Lippizaner Horse Show or training, if you like horses.

Maybe you are already here, but I somehow missed this question.

My top 10 in Vienna:

1. Schonbrunn Palace (interior, gardens and carriage museum)
2. Belvedere Museum (to see Klimt's Kiss and other works of art)
3. Stephansdom (pay to go up the elevator to the North Tower)
4. A walk down the Graben and Kohlmarkt, through the Hofburg and into the Volksgarten (roses are currently very much in bloom) ending at the Rathaus
5. A coffeehouse (Gerstner, Diglas, Pruckel, but not Sacher or Central) for Apfelstrudel
6. Kahlenberg (take the 38a bus to the top and stop at one of the many buschenschanks or heurigen on your walk back down to Nussdorf following the trail marked Stadtwanderweg 1)
7. Rent a boat from Marina Hofbauer and motor slowly along the old arm of the Danube (Alte Donau)
8. Wien Museum - free and fascinating
9. A market (I avoid Naschmarket but love Karmelitermarkt on a Saturday; there are other great markets too)
10. Austrian National Library (Prunksaal) is an absolute glory

My next tier/alternates would be the following five:
1. Karlskirche
2. Kunsthistorisches Museum
3. Leopold Museum
4. Opera House
5. Jesuit Church (Jesuitenkirche)

Notice that several places listed above are not even on my top 10/15.

Kaisergruft (Kapuzinerchurch Oldtown) incl the Gruft (grave) from Kaiserin Elisabeth.

When will you realize? Vienna waits for you.

Some really great responses to your original post.

I'll add that Rick's walking tour https://www.ricksteves.com/watch-read-listen/audio/audio-tours/austria-germany is a great introduction.