The garden at Ninfa (from the Great Gardens of Italy book to accompany the series)
There were many gorgeous gardens featured in the series, but my absolute favourite was the garden at Ninfa. This is about 30Km south of Rome and was created around the ruins of a Medieval town. Monty himself described it as "the most romantic garden in the world" and even though I haven't seen it in the flesh, it looked magical on the programme. If I ever get the chance to go to Italy (I have been once but it was a school trip and didn't include any garden visits), I would love to visit Ninfa and some of the other inspiring places.
The last programme is available on iplayer: http://www.bbc.co.uk/iplayer/episode/b010y067/Monty_Dons_Italian_Gardens_The_Veneto_Lucca_and_The_Lakes/