We will be arriving after an overnight flight and would like to take a bus to Siena. Sadly, we will miss the 10:45am direct bus. So it looks like the Flix bus is our best option. Has anyone used this recently and can tell me how to catch it?
Take the train or taxi to Rome Tiburtina Train Station
Outside of front left of Rome Tiburtina Train Station there is area where you can catch Flixbus.
Here is the route from the airport taking the train:
https://goo.gl/maps/uWWEBAWdLkAJYMTh7
Download the FlixBus app and use it to buy your ticket. It might save you some € instead of buying it onboard. Very easy to use and convenient app.
We took the Flixbus from Tiburtina to Siena and back again last year --- it was fine, a very nice clean coach bus. The only thing I would say is that when you exit the Tiburtina metro station, it is not at all obvious where the bus station is (and we thought we were looking for just a bus STOP, not the large, open-air bus station that it is). We had to go up to street level, cross a street, and then walk around a bit. So leave plenty of time to find your way and also to get a good seat on the bus. Also, although there's a toilet on the bus, you may want to use the bus station's restrooms or a nearby bar --- on our trip, the bus toilet wasn't working going to Siena.
Then, you may know this already, but the bus will leave you at the train station in Siena. From there, you can either get a taxi or you can take a long series of escalators up the hill, then walk several blocks to get to the center of Siena. We greatly enjoyed the escalators and the walk, but not everybody would after a long plane trip (we were only coming from Rome).
Yes, get the app.