Whereas all Italian hill towns have steep streets that can be treacherous when wet, Orvieto's streets are a little steeper and their surface a tad more slippery than others. Orvieto was the one hill town that we observed an injury from walking on streets. A teenage girl was walking with parents on one of the streets in the old town and had a serious fall. While she could get to her feet she was badly bruised and had trouble walking. This was during a light afternoon rain.
Best to take your time and purchase a good pair of shoes with preferably a steel bar for extra support and protection against falls.
I cannot stress this enough: stick to the rules and obey to any parking sign! Apart from that, Orvieto is trying to get the traffic out of the city and offers convenient parking outside and free shuttle busses. Otherwise, the police is everywhere and will come to issue tickets if a car does park or even stand where there is no parking or parking for residents only.
While driving around, stick to the speed signs. Yes, even if this is Italy which is famous for very much chaotic and fast traffic: police cars are standing along many roads and take the speed, no matter if it is a highway or a tiny street. I saw several police cars on the roads around Orvieto.
Parking at Campo della Fiera is for example only 0,50 € per hour or 5 € for 24 hours! Now how good is that?
Do not stay at the Locando del Lupo hotel unless you want to be scamed. I made a reservation and paid a 10% deposit (which is not uncommon in Europe) for a 2 week long trip for 7 people but was told when we arrived that we could not stay there and that my expensive deposit would not be refunded. Very sketchy. Avoid like the plague. We ended up staying at the Hotel Posta which was very nice and legitimate.
If you choose to drive to Orvieto I would recommend you park in or near the station below the town and then catch the tramcar up into the town. Parking in the small center is not easy and there are a ridiculous number of parking officers. The tramcar is fun and you can walk around orvieto without worry.
While I was gazing at the facade,I fell off the stairs of the dome because I think there is not enough width of the platform compared to the height of the facade.