Check out Tenuta di Spannocchia in Siena, Italy, pictured above:
A working organic farm that produces its own meat, eggs, grains, vegetables, honey, wine and olive oil. Guests can rent their own farmhouse for a week or stay for a few nights in one of two bed and breakfast facilities. Visitors are welcome (but not required) to learn about and get involved with the farm's day-to-day operations, which rely on sustainable farming techniques.
Spannocchia is home to one of Tuscany's first natural waste water treatment systems, and guests are strongly encouraged to participate in the farm's composting and recycling programs. Housekeeping and linen changes are done once a week. Doubles from $97 (farmhouse, based on weekly rental) or $108 (bed and breakfast) per night.
Read the entire detailed list and link to each location's website here.