Turin

Number of days depends on what interests you. Have you had a look at the various sites in Turin? Many palaces of the Savoys in the city and surrounding area, like La Venaria Reale, the National Museum of the Automobile, Cinema Museum, Egyptian Museum, etc. you can probably see two of those sites per day. Also a good city for just walking, shopping.

We like NH Hotels and there are several in Turin.

Two nights at least.

This is an excellent hotel and the prices are very reasonable.

https://grandhotelsitea.it/

I agree with everything that Laurel said and would add "eating" as another great thing to do in Turin. Also an excellent city for aperitivi, coffee, and chocolate.

Turin is chock-full of Art Nouveau architecture. I know I would need several extra days to see that.

I was there last year. Loved it. I stayed at the Grand Hotel Sitea (linked above) - which was great. How long depends on what you like to do.

Not a foodie, but food was terrific.