We just got back from Tuscany (went there for a week after riding with Riviera Bike). We stayed in a beautiful hill-top village (yes, there’s loads of them) between Lucca and Castelnuovo di Garfagnana. We pretty easily found some epic off-road routes and if you don’t mind a bit of a hike-a-bike you can have some proper adventures on the long-range paths, there are maps in most of the villages.
Check out http://www.bikemap.net for loads of routes around there, handy of you have a GPS.
There are some published MTB routes around Portofino and the Cinque Terre a little further north.
Ride, coffee, ride, beer, piles of food, sunshine, scenery, beer, wine. I reckon you’d be gutted if you didn’t take your bike. Enjoy.