Guided Day tour of Siena but staying at a Florence hotel

Jeff, Margo-I don't know if a "walking tour" is what you have in mind, and we never did this but in researching a couple years back I found Siena Walking Tours, excellent reviews on Trip Advisor. There's a bus from Florence.

http://www.sienawalkingtours.com/#_=_

http://www.tripadvisor.com/Attraction_Review-g187902-d2356445-Reviews-Siena_Walking_Tours_Private_Guided_Tours-Siena_Tuscany.html

If you are up to a long day and want to see more than just Siena, I can highly recommend the Walkabout Florence Best of Tuscany Tour -- https://www.walkaboutflorence.com/tours/best-tuscany-tour. They have other tours, but I haven't been on any of those. Even our 5-year old granddaughter enjoyed it.

The above tour looks like a solid value, and you'd have a great time.

The alternative would be to go across the street from the Florence train station (to the right of McDonalds) to catch a bus into Siena. When you arrive, you'd need to meet up with a walking tour. .