When I walked with a friend from Siena to Rome last summer, the one place that really stood out for me was Agriturismo Passalacqua. It is outside the small town of Gallina, which was about 4-5 days south from Siena. It is situated on a hilltop, looking down into the valleys on three sides, and you could see Radicofani up on the hilltop way off in the distance. They served us a wonderful dinner and breakfast sitting out on a picnic table. We had a full suite, with living area and kitchen. It's not cheap, but it would be a great place if you are looking to splurge. I can't remember the names of the couple that own the place, but they took good care of us.