Unique things to do in Firenze?

Not in Firenze, but have you been to Arezzo or Sansepolcro?

In Florence see if the gregorian chants are still taking place at San Miniato al Monte and enjoy the climb.

There's also a fascinating cemetary there.

Maybe take the bus up to Fiesole, which is a pretty little place with a well preserved Roman amphitheater (surrounded by Etruscan walls).
If you don't mind a bit of walking you can head out to Monte Ceceri to visit the site of Leonardo's first experimental test flight in 1508
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If you enjoy opera, or even if you think you don't and are open to giving it a try, I would suggest checking out the Opera at St Mark's Anglican Church. My DH and I have attended twice, it's a lovely experience. All profits to a charity in India that supports orphaned children. The church is beautiful andthe performers are professionals. if you get a front row seat, you will be about 15 feet away from the singers. The location is on Via Maggio in San Spirito area. My DH dislikes opera, but enjoyed both our visits immensely. Price is reasonable as well, 25-40E per person depending on which opera you select.

A gondola ride

Haaaave u done this? - Cafe in Bardini Gardens

https://www.walkaboutflorence.com/what-to-do/caffè-belvedere-bardini-garden

The Bardini Gardens are lovely, and not many people seem to go there. You climb up through the gardens, and at the top you go out and cross a road to go into the Boboli Gardens on the same ticket.

These are all things I'll check into...well, maybe not the gondola ride ;). I thought about Fiesole already so I'll revisit that idea. The opera is a good thought, for me at least. Haven't been to arezzo or the other town. I'll check the transportation connections. Already planning on seeing the gregorian mass, thanks for the reminder, Claudia! We planned on it the last couple times and the days got away from us. The gardens aren't really my thing but thanks for the suggestion.

Going to the gardens is really just to get away from the heaving mass of humanity that is central Florence nowadays.
It's a nice breather in a quiet space.

Have you been to the Museo San Marco? The Palazzo Davanzati Orsan St. Michele?

The central market is a great place to wander and we had a really good lunch at a stand there (pork sandwich). You could spend a few hours there just looking at all the goods for sale (or buy them LOL)

I see quite often suggestion for opera evenings with singers and piano, but I never see suggestion for the real thing, that is opera at the opera house with full stage, full choir and orchestra and extras. All Italian cities have opera seasons - there isn't only La Scala and Verona - and often tickets are not that expensive if you are not looking for the few gala performances. Florence has a brand new opera house, one of the few modern buildings in town, this October they have Puccini's Rondine and Donizetti's Elisir d'amore (in a very strange production, I concede).

Kaeleku, we will be staying and visiting several other areas of Italy on this trip but we love Florence and like to have some time to just "be" there. I just wanted to also try something I hadn't done yet in the area and was open to suggestions.

Wendi,
If you are a history buff or have any relatives that fought in Italy during WWII, there is a fabulous American cemetery 7 miles outside of Firenze. Think of Arlington with rolling hills, umbrella pines and cypress trees. Magnificent! Also, there is the Leonardo DaVinci museum in the small hamlet of Vinci, which is fascinating. Engineering students have recreated Leonardo's instruments using his guidelines and drawings. Although DaVinci is so well known for his art, he was an inventor of many items that made living in his time easier for the common people, not just the wealthy. He invented a bobbin that made sewing easier and a device for making it easier to get thread from wool. Both places are great. Have fun!

Thank you all for the great ideas!

Hooray for going back to Firenze! It's amazing how you can find something new and spectacular every time you visit. Last time I went I visited the Galileo Museum. Its a great break from the crowded squares, is super informative, and has a huge collection of scientific artifacts from the origin of the study of science that was happening in Europe at the time. Plus it has some of Galileo's fingers, if your into that sort of thing!

Get hold of this book:
The Cognoscenti's Guide to Florence
by Louise Fili & Lise Apatoff
It's filled with things to do and see in Florence that you would have never thought of.

And more great ideas! I'll check out that book! And we will look into the galileo museum as well.

Congratulations on returning to Firenze! I never tire of this magnificent city either!

Last Nov., I attended an amazing art exhibit at the Palazzo Strozzi. (The exhibit was on the works of ai weiwei.) I notice that this month, Palazzo Strozzi will be hosting a new exhibit called The Cinquencento a Firenze. https://www.visitflorence.com/florence-museums/palazzo-strozzi.html Enjoy your time in Firenze!

Wendi, if you haven't been there yet check out Piazza Santissima Annunziata (it's very near San Marco). This is a wonderful square with one of Brunelleschi's earliest commissions on one side: Ospedale Degli Innocenti. This was one of the first foundling homes in the world, and they've re-opened (was unfortunately closed when we were there) with new exhibits that are on my own list for next time.

https://www.visitflorence.com/florence-museums/innocenti-museum.html

On one of the other sides is Basilica Della Santissima Annunziata, with an unusual entry cloister decorated with marvelous frescoes. You'll find works both outside and inside the church by del Sarto, Rosselli, Lippi, Vasari and others.

Lastly, look down the street from the square for a different perspective of Brunelleschi's greatest achievement (not my shot but I have one much like it):

http://l7.alamy.com/zooms/38051db613e84fba8d371e48bf27300b/santesshima-annuntsiarta-church-church-square-duomo-florence-italy-b1jbb3.jpg

Take one or more art history classes at the British Museum --- in October it will be Early Renaissance, excellent lectures and visits. Stay in a completely different part of town from where you have stayed before --- this time, we are living a few steps from Piazza Beccaria on the pedestrian-only street Via Borgo la Croce and loving it. For a day trip, go to Pistoia, half an hour by train, and don't miss the Cappella del Tau if you like slightly odd 14th century frescoes.

Christine, we already checked into what would be going on at Strozzi while we're there. We always seem to catch something interesting at that place! And thanks for the other suggestions, everyone. I'll definitely check into that little town!

yes, Fiesola is a beautiful little town with a fabulous view of Firenze and the sunset from the restaurant on top of the hill.

We are currently in Florence for 8 nights and went to the Museo Bardini today. There were 3 other people in the museum while we were there so it was a lovely respite from the tourist chaos in other parts of the city. The current exhibit is wonderful - pieces by contemporary artist (Glenn Brown) are interspersed with the permanent collection and it's been curated extremely well. Highly recommended, as is the book Cognoscenti's Guide to Florence. We are having a lot of fun finding their recommendations for unique shops around the city . Her restaurant recommendations are a little too traditional for us. Food is very personal so YMMV (your mileage may vary). We've had good success with Spotted by Locals - an app. which has lots of other suggestions beside restaurants.

Gallileo Museum is terrific..

We visited Firenze last March with the same goals - to do things we haven't done on previous trips. In the city, we visited Santa Croce, a beautiful church inundated by the Arno in the historic 1966 flood. We also did two out of town trips - one to Bologna for the day and the other to a winery/agriturismo in Greve in Chianti for a cooking class, wine tasting, and a great meal. You can catch a train from Firenze SMN to Bologna; the trip is only about 35 minutes. Bologna was great - no tour groups, just Italians living their daily lives. There is lots to see in the Old Town and the food is great. For the agriturismo/winery, we went to Vignamaggio, which is the ancestral home of the 'Mona Lisa', with a villa originally built by her family (Gherardini) in the 14th Century. Several others on this forum had highly recommended it and you can add us to that list. The cooking class was fun, we had three different wines with the meal, and the scenery was amazing (we ate our meal out on the patio overlooking the olive trees and vineyards). Vignamaggio is located about an hour drive from Florence (we hired a driver to take us there and back). On the way back, we stopped at the Florence American Cemetery, where 4400 American soldiers are buried (including some from my late father-in-laws regiment, the 442nd Regimental Combat Team/100th Infantry Battalion). Like other American Battle Monuments Commission Cemeteries, the grounds are impeccably maintained and the Cemetery personnel are very welcoming. Lastly, I didn't see Pisa on your list of places you have been, and would definitely recommend seeing the 'Piazza dei Miracoli'.