There are countless sites to visit in Vienna, and just as many websites to view in preparation for your trip. I'll start with Evelina's Foot On The Road site for photos and information about palaces most visitors see in Vienna: https://footontheroad.com/palaces-in-vienna/
Here is a list for you:
Schönbrunn Palace
Hofburg Palace
Belvedere Palace
Liechtenstein Palaces
Albertina Palace
Palais Ferstel
Palais Obentraut
Palais Pallavicini
Palais Palffy
This is another useful and enjoyable site, Urban Traveler: https://www.urbantravelblog.com/best/palaces-in-vienna/
This is the Earth Trekkers site with their bucket list of what to see in Vienna: https://www.earthtrekkers.com/top-ten-vienna/
This site is Anywhere We Roam, and this page features Vienna: https://anywhereweroam.com/things-to-do-vienna/
This is Moon And Honey Travel with their hidden Vienna gems: https://www.moonhoneytravel.com/vienna-hidden-gems/
This is the Vienna page of the Just A Pack website: https://www.justapack.com/off-the-beaten-path-vienna/
The Vienna hidden gems page of the 22 Places website:
https://www.22places.com/vienna-hidden-gems/
The Stage Door to the Vienna State Opera House.
Its commemorative plaque below.
Hotel Sacher
The famous Opera toilet. With music.
As one of my favorite poets, Fernando Pessoa, author of The Book Of Disquiet, gets two appearances in this post.
This Radio Funk Haus ear gets two appearances, as well. You know you're in Europe when the cafes are named after poets from other countries, and there are statues on posts of Seraut-inspired ears.
And there are shops dedicated to selling only gloves.
And Italian ice cream shops, or Gelaterias.
From the site creators:
"If there’s one thing we know, it’s that we all like to be in on a secret. And we’re about to expose some. Well, many of you will know these 14 places, however, this is a list of places in Vienna that aren’t so widely known. To the regular visitors of these places – please don’t be mad, we just want to share all the cool places we’ve discovered over the years with fellow lovers of Vienna."