If you will be in northern Italy in September or later, you can tour the quarry where the pink and white marble that covers the Duomo was obtained. The Candoglia quarry will have tours on Tuesdays, Fridays and Saturdays, beginning 03/09. You can read more and find a link for reservations here:
https://www.duomomilano.it/en/article/2022/06/16/the-origins-of-the-duomo-candoglia-quarry/439/
We were just in Milan specifically to visit the Duomo and climb the steps to the roof, to see the details of the architecture and carvings up close. It was a great experience. If you can manage 250 steps I highly recommend it. Otherwise, you can take an elevator. The steps are safe and secure, and not a challenge to the claustrophobic nor the height averse ( I am both).
I was particularly struck by the beauty of the stone, and wondered where it was quarried. We are now at Lago di Garda and saw a lot of pink and white stone at Sirmione, at Spiaggia Jamaica (where my husband went swimming—google it) so I wondered whether this was the source. Answer is no, the quarry at Candoglia is very close to Lago Maggiore, specifically near the village of Ornavasso, which one can reach by train from Domodossola.
We cannot make time to visit the quarry on this trip (have to plan for another time) but I want to mention this in case anyone is interested in such things.
Ciao from Desanzano, Lago di Garda