tmac - Sounds like a great trip. Here's some info on Ostia from my blog
http://www.somuchmoretosee.com/2014/...q=ostia+antica

If you decide to see something closer than Orvieto and have any interest in modern architecture we found EUR fascinating.

http://www.somuchmoretosee.com/2014/...ase.html?q=eur

Here are the rest of our Rome suggestions on the blog incase they're useful.
http://www.somuchmoretosee.com/search/label/Rome

Willit, I didn't say that Tivoli was "hard to get to". I said it was "a bit more complicated" to get to than some of the other destinations mentioned. And that's obviously the case. Lots of tourists make the trip on their own, but it's not duck soup. Tiburtina station isn't in the center of Rome, and the train station in Tivoli is more than a mile from the center of town, where the Villa d'Este is. There's also a bus to Tivoli, leaving from a bus depot at the Ponte Mammolo metro stop. This takes you right into the center of Tivoli, but the Ponte Mammolo metro station is a bit of a hike from central Rome, and the bus takes longer than the train.