As Iachera said, the railway mostly runs at least a couple kilometers inland, therefore you won’t be able to see much of the Tyrrhenian Sea. The sea is in fact the Mediterranean, however each section of the Med has also its own name to differentiate the different areas (Adriatic sea, Tyrrhenian Sea, Ionian Sea, Aegean Sea, Ligurian Sea, Sea of Sicily, Sea of Sardinia, and so on).
The only sections of that railway that are close enough to the coast to be able to see it, are south of Livorno (from Ardenza to Rosignano), near San Vincenzo, then south of Civitavecchia between Civitavecchia and Santa Marinella. The rest is a bit inland and you won’t be able to see the water.