Consider a visit Pienza (it is close Montepulciano. Pienza is a little and
peaceful town in Renaissance style (visit the cathedral, the Piccolomini
Palace and the little museum of the cathedral). If you didn't visit before,
visit Perugia city (the capital city of Umbria Region), Assisi and Gubbio
(lovely medieval town).
Not too far from Orvieto (20 km) there is an interesting little ghost town:
Civita di Bagnoregio (look for Bagnoregio on the map). It is situated at the
top of a roach and the houses are built in tufa stone. You can visit the
hamlet and the church. I strongly suggest you to visit this estrange town
(it is not crowed by tourists)!
Along the sea there is the Mount Uccellina Park. It is a very nice park
(with many pathway) but, unfortunately, I don't know if it open in March.
Aroum Montepulciano there are many lovely place (town, abbey and some
archaeological dig) but I think that this place are showed in a well
guidebook of Toscana and Umbria.
Enjoy, Marco in Milan (Italy).