Prater is a famous fun-park in Vienna, surrounded by a huge park. At first it was only for the nobility until Kaiser Franz Josef II. made it open to everyone in 1766. There is also the famous ferris wheel "Riesenrad" if you fancy a ride!

https://prater.at/park-information/

https://wienerriesenrad.com

There are tons of museums and galleries in Vienna. Here are just a few:

Albertina - https://www.albertina.at

Kunsthistorisches Museum - https://www.khm.at

Sissi Museum - https://www.sisimuseum-hofburg.at

Schloss Schönbrunn - https://www.schoenbrunn.at

Schloss Schönbrunn has a huge park is also a great activity!