Some useful information from Lookupatthesky (Original article here)
If you are driving in Italy take your disability parking permit with you. You will be able to park free on the street or in a parking building. You may need to produce photo identification showing the disability or handicap symbol when you use a parking building. In some parks you will need to get your parking chit validated. Italy is trying to cut down on white collar crime so you will nearly always be given a ticket (for parking or for entry to an attraction) that has to be validated. If all the designated parking for the disabled is being used you can use other parks for free. The only parking places to avoid are those disabled parks that have a number because they are assigned to a specific person.
Cities and towns in Italy offer people with disabilities and a companion free entry to all civic and state owned attractions. Many privately owned attractions offer free or discounted entry to people with disabilities.
People with disabilities do not need to queue for tickets to attractions but can go straight to the ticket office. I suggest either getting the attention of a security guard or going to the ticket office for tour groups and people with reserved tickets. You may need to produce photo identification showing the disability or handicap symbol. I used a New Zealand Operation Mobility Card, some countries have parking permits with ID, otherwise I suggest a letter from your doctor with an Italian translation.
It can be difficult to visit towns in Italy because the roads are cobbled, and often steep. However, if you are prepared to have a helper, it is well worth the effort and inconvenience. Also, if you are prepared to accept the help of strangers and explain how they may help, Italians will go out of their way to help and leave your dignity intact. You don’t have to speak Italian. Body language works, and if you speak English, most Italians understand you well enough.