If you’ve just gotten off at Fiumicino and want to catch the train to the Maremma, all you need to do is wander over the train station in the airport and catch the train to Roma Termini.
From there you can hop on the Rome-Pisa line all the way to the Maremma.
There are four Trenitalia train types – direct, regional, Intercity and Eurorail. You need to book Eurorail tickets before you get to the train station.
Make sure you check that your train stops at the stop you want to go to.
The Rome-Pisa line has stops in Albinia, Orbetello, Alberese, Talamone, Capalbio, Scarlino, Follonica, Tarquinia, Civitavecchia and Grosseto.
If you’re coming from Pisa, you can also catch this train.
If you’re coming from Florence, you need to catch the Rome-Florence line, get off at Pisa Centrale and then catch the Rome-Pisa line.
If you’re coming from Siena, you can catch the Siena-Grosseto line direct to Grosseto.
Once you’re at your chosen city, you can rent a car (if you’re in Grosseto or Follonica) or catch the bus to your agriturismo.