2 days in Florence and 3 in Chianti (Tuscany)
Ciao aaceti!!
Here I am!

Sorry for the delay in replying but I'll do my best to provide some tips and suggestions for your trip!
A
surprise 20th anniversary vacation to Italy sounds awesome! Your husband, and you, will definitely enjoy yourselves tremendously

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Have either of you been to
Florence in the past? I'd definitely you Florence at least two days so maybe 9/12-13 would be ideal. Florence is the capital city within the region of Tuscany so you'll already be in Tuscany as soon as you arrive here. The best solution is indeed to take the train from Venice to Florence (check train timetables on
www.trenitalia.com - it might not yet show ones for September but they generally stay pretty much the same year round - you don't need to book ahead of time unless you're thinking of using the fast trains, those do require reservations and thus better to buy a bit ahead of time). Once in
Florence rent a car to drive yourself out to
Chianti - the wine region is just south of Florence and occupies the entire area between Florence and Siena. It is the most widely known area in Tuscany and is ideal for spending time in the wine region.
Do you prefer to then join a tour for a day or two (9/9-9/11) or to drive yourself around the region at that point since you'll have your own means of transportation? It is small distance wise and you can decide to visit a winery or two and then spend the rest of the time enjoying great lunches and dinners out while exploring the small hilltowns in the area - you can visit
Greve in Chianti, Panzano in Chianti,
Castellina in Chianti and
Radda in Chianti on your time and schedule.
With your own car, you can definitely not worry about getting to your vacation rental - public transport is almost nonexistent within Chianti so a car is really a must for staying there.
Some romantic places I'd recommend for your stay:
Fattoria Viticcio - just outside Greve in Chianti, a wine estate with apartments where you can do wine tastings and tours of the estate
Chianti Suites - apartments in a restored farmhouse with pool
Palazzo Malaspina - very romantic B&B in a small fortified medieval village
How about a stay in a tower of a medieval castle? Take a look at
Castello Sonnino!
These are just some suggestions to get your search started - the pages have direct links to the official websites so that you can contact each of the places directly and get the best rates and availability directly from them. If you need or want some more ideas, let me know!!
Once you head back to Florence, you can return your car as soon as you're back in the city since you don't need it at all once you're here. Florence is small and walkable - if you stay in the center, everything is 15-30 minutes slow walking distance away. For ideas of places to stay in Florence, take a look at
Florence Accommodation.com. If you're looking for something specific, let me know and I can point some out in particular that fit what you're looking for.
You'll have a great time in Tuscany and Florence (and Venice)!! Have fun planning the trip on the sly
