I traveled with friends to Siena and San Gimigano for a short day trip. I've been to Siena recently, but I didn't mind coming back because I loved it there. I'll also put some pictures from the previous trip there.
We arrived to San Gimignano first, I knew that it's a touristy place, but I completely understand why. The city is stunning and the best part is the surrounding panorama, the rolling hills of Tuscany is just so eye catching. I only had an icecream there and luckily arrived before the big 50 meters tourist line estabilished itself for the day. I highly recommend going to Gelateria Dondoli and try out their fior di latte and fig ice creams, just out of this world.
San Gimignano similarly to other tuscan villages, has their own towers froknthe medieval times and if you are lucky you can meet with the people living in them.
Siena is a stunning city, very similar to Firenze in vibes, but still has it's distinct feeling. The city offers quite a lot, the main piazza with the townhall is overwhelming in size, and the Duomo there is one of the most stunning churches I've ever seen. It's really worth the ticket's price. I recommend just wandering around the districts, with each one having their own flags and identity.
To eat I can highly recommend Osteria Nonna Gina, with their hand-written menu and secret recipes from the grandma herself.