Exit the Termini railway station with the railway tracks behind you taking the RIGHT hand exit : you will find yourself in Via Marsala, cross the road and go ahead to your left, turn right at the first street. Now you are in Via Vicenza. Go straight ahead for 250 meters and turn left in Via Villafranca the hotel is at number 1.
From Rome Fiumicino Airport there are many ways to reach the San Marco Hotel: by private taxi; by rented car: when leaving the airport follow signs to Roma Centro. Once you reach the ring road (Gran Raccordo Anulare), drive in the direction of Naples and continue until exit 21 in Via Casilina and then follow the signs to Roma Centro. Drive down Via Casilina until Piazza di Porta Maggiore, continue towards the Termini Railway Station by driving down Via Giolitti: go around the station square and take Via Marsala on the right; the "Terravision Shuttle" bus will drop you at the Termini Railway Station. From the station square take Via Marsala, which runs along the right side of the Station.
Take one of the coach companies from outside the airport which will take you to Via Marsala at Termini station for around 6 euros. The most famous of these companies is Terravision. On arrival at Termini, simply follow the directions above.
From the Ring Road (Grande Raccordo Anulare), take the exit Roma Est-Tivoli and follow signs to the centre of Rome. Turn into Via Tiburtina and continue up to Piazzale Tiburtino, drive under the underpass and then turn right into Via Giolitti, which arrives directly in front of the Termini railway station.