Two Nights in Graz-Tips?

I'd love to visit the museum dedicated to Johannes Kepler. He is a giant in the history of astronomy. In the 16th century he developed his 3 laws of planetary motion and laid the groundwork for the field of physics and Newton's work.

The Armory was a big hit with our young son, years ago.
https://www.museum-joanneum.at

Looks like the link goes to a group of museums, not just the Armory.

I will be in Graz next October on my way to the Best of Adriatic tour, so hope to hear some good ideas, too. Graz doesn't get much attention.

I sort of stumbled through Graz several decades ago without significant planning. (It was pre-internet, and guidebook coverage wasn't great.) I thought it a really handsome city and hope to get back there when it's geographically convenient. It was a great place for walking around, so allow time for that.

Another city I loved on that trip was Ljubljana, and we all know what has happened to tourist levels there.

If you like horses, Piber Lippizan Stud is nearby. https://www.srs.at/en/lipizzaner-stud-piber/ I haven't been there but it's on my want-to-see list.

The outline of a Graz-Klagenfurt-Lesachtal trip is hanging out on my hard drive. Graz looks like a great place to me, and I am eager to go there.

I have come to kind of like the Culture Trip website for some initial exploration of travel locations. Articles are headlined with breathless titles like "5 Galleries You Have to Visit in Graz" and there are a lot of "top 17 things to do"-type articles, but it often gives me a good "jumping off" point for exploring a new location.

The Culture Trip site for Graz: https://theculturetrip.com/europe/austria/graz/

Really enjoyed Graz - a bit of a hidden gem in my opinion and you won't have any trouble filling a day or two. Beautiful old town, lots of nice outdoor cafes to enjoy. The center is definitely walkable, although the main station is about a 20 min walk from central Graz so I'd recommend the tram for that part. I believe they also offer free trams in the central old town area.
Definitely visit the Schlossberg/clock tower for great views over the city. The old town itself is worth a long wander around - lots of picturesque streets and squares (Herrengasse, the Hauptplatz and city hall, Glockenspielplatz). If it's raining, there are plenty of interesting museums. The city has a good tourist website which can give you ideas.
As for food, there are plenty of places for traditional Styrian dishes (and wine!) - we enjoyed Herzl Weinstube, Altsteirische Schmankerlstube and Glöckl Bräu. Der Steirer is also really nice and a bit pricier - regional food with a shop attached (reservation recommended as it's also popular with locals). I also often like to eat at museum cafes, and the Kunsthaus cafe is excellent for breakfast or lunch. The building is very quirky and the food is good value and quality.

Thank you all for the wonderful tips. Actually really looking forward to seeing Graz.