We plan to stay in Tuscany for 5 days the end of September. What are must sees?
Tuscany is quite large
Florence for starters
Tuscany is indeed a large area, and positively crammed with must sees. However what is a must see for one person is bored to tears for another.
What are your interests? How will you get around from place to place? Where are you before and after Tuscany?.
Perhaps start with reading the Tuscany section of the Explore Europe subforum. Then get a guide book or 2 to see which must dos appeal to you.
With five days I would spend three nights in Florence and visit the Uffizi Gallery and Michelangelo’s David at Accademia. You’ll need to buy tickets for the former two months out.
From Florence I would take a direct bus (1h 15m) to Siena and sleep there two nights. I would rent a car in Siena and get on the Sienese Crest Road and drive past Montalcino and continue on to Montepulciano for the day.
Take your pick:
https://www.visittuscany.com/en/