Bagno Vignoni

You don't need to go far away to be in paradise...
Ahahahah! It sounds like one of those fancy, shiny, glossy headline...but it's true!!! Works for me at least...living in Italy.
"Adler Thermae" is one of those places you'll never forget.
A bit expensive, but worth every single cent!
Laying just below the town of Bagno Vignoni, this place has it all!!!From high quality rooms, to a great restaurant...not to mention the infrastructure! And if you get bored of all this relaxing, you can take a break visiting the many ancient towns surrounding the area:
Castiglione d'Orcia (just in front of the SPA you get a wonderful view of it bathing in the pool), Bagno Vignoni itself, San Quirico, Pienza...they're all part of the "Val d'Orcia" nominated heritage of the world by UNESCO. But don't only stick around the main path!!! If you'll be a bit curious you'll find places where the time has stopped and won't even believe your eyes. Just to mention a couple of spots, Monticchiello e Castelluccio are two good examples of what I'm talking about.
And for those who like sitting around a table and enjoy great tastes, "Il Vecchio Forno" in San Quirico d'Orcia is totally the place to go. In Tuscany you won't have so many problems spotting good places to go out for dinner and remember it for ever, but trust me this is a place to visit!!!
Another impressive restaurant (the food is above the average, but the location is over the top) is "La Porta" in the wonderful Monticchiello. Since it's a small place and the tables are not so many (especially on the terrace), try to make a reservation...and you won't be disappointed.