One day in Milan

Milan is a beautiful city! So excited for you! You will love it! you MUST see the cathedral! Its truly a treasure and I'm certain the sight of it will truly take your breath away.
I'm going to dig deeper and ask you what are your interests? Is there anything in particular you seek out while in Europe? I'll let the RS group answer to that as well.

Ill tell you what I did the last time I was in Milan for 4 days in 2022 and you can decide if it sounds interesting?

We stayed at the Gran Duca du York hotel and it was nice, not super fancy but clean, nice, great breakfast, kind employees and close to the cathedral and the art museum. Very nice and somewhat budget friendly while being super nice.
We did a rooftop tour of the cathedral which we loved! Viator
We went to see the "Last Supper" on a tour I booked thru Viator. WOW! If you are interested in art, this is a goal! It surprised me and I wont say why but I guess you just have to see it for yourself.
You might look for a tour of the city on Viator since you are only there for a day!
We ate dinner at a family run place. When you eat dinner in Milan, know that they eat dinner LATE! Unfortunately I cant remember the name of the place- but you are in ITALY. get off the beaten path, is my recommend.
Walk the city around the cathedral around sunset. It's very lively.
Last-if you are interested in music- go to the Opera! check ahead if there is an event the night you are there. You must get dressed up. Its a once-in-a-lifetime experience.

I seem to keep suggesting "Viator" but I don't work for them. ha! But you can look at this site-its a clearing house for tours that might spark your interest! if you only have a day- and i think its nice to get the most out of your visit! I love Milan and I hope that you have a wonderful trip!
Lisa

The most recommended sights are usually the Last Supper and the Duomo rooftop terrace. You do not need a 3rd party tour company for either, though if direct booking on the relevant websites are sold out, people do sometimes find tickets through tour vendors. The English tour through the Last Supper direct booking website was excellent. Last Supper tickets need to be reserved as soon as they become available for the date you need. Duomo tickets can be reserved closer to the date or sometimes bought on the spot (but best to reserve if you only have 1 day). I found the RS guidenook and especially the free RS audio tour of the Dumo and area around the Duomo very good. Staying near Cadorna Station and walking everywhere, during one full day in Milan, I found it easy to cover the Last Supper, the Duomo rooftop and inside the Duomo, Galleria Victorio Emanuel (landmark istoric shopping gallery), La Scala Opera house (just the outside), as well as the 4th century Basilica Ambrogoana on my way to the Last Supper in the morning, and a walk around the Quadrilateral area (designer window shopping) in the late afternoon. It would also be easy logistically to visit the Pinacoteca Ambrosiana (art museum) which is a couple blocks from the Duomo.

Who is “we”?
When is your trip?
Will you just be arriving after an overnight flight?