Trastevere is just on the other side of the Tiber with respect to Rome city center and few miles from the Vatican.
From the Highways:
If you come from the north of Italy: take the "Grande Raccordo Anulare" (GRA), the Ring Motorway of Rome, and exit direction Aurelia/Città del Vaticano (Vatican City).
Follow all the Aurelia road untill you will see a big square with a Mc Donald's on your left (the square name is Piazza San Giovanni Battista De La Salle). Turn right on Circonvallazione Aurelia and go straight always following the main road Via Gregorio VII.
Pass under the arcades of the railway and go straight on.
Reach Via di Porta Cavalleggieri where you will see a gallery.
Beware! After the arcades of the railways you might be forced to turn right on Via del crocifisso. In that case, turn the 3d left (Via Niccolò III) and then the second left (Via della Stazione di San Pietro). Finally the third right (at the very end of the street) is Via di Porta Cavalleggieri, take it untill you reach the Gallery.
Take the Gallery and turn right without crossing the Tiber.
Follow the road along the Tiber (Lungotevere) untill the very end. You will reach a red light: just turn right and follow the tramway rails until you see on your left a Cinema called "Nuovo Sacher", take the first right. The square in front of you is Piazza San Francesco D'Assisi.
If you come from the south of Italy:
Take the GRA direction fiumicino Airport, exit and take the motorway for the airport on the direction of the city center, opposite to the direction of the airport.
Exit Magliana/Trastevere/Centro and take Via della Magliana untill the end.
Turn right on the Lungotevere untill you arrive to a red light and you will see a bridge on your right.
Turn left on Viale Marconi and go forward untill the end, pass under the railway arcades and go on straight on Via Ettore Rolli, then Via Portuense.
After 3/4 streets on your left, you will reach a sort of square (there is a supermarket GS on your right handside), take the big road on your left (Via Ippolito Nievo) and turn right when you cross Viale Trastevere.
Follow the tramway railways untill a red light where part of the railways go forward and part of them turn right (there will be a huge white building on you left handside, that's the Ministry of Education).
Follow the railways that turn right and you will pass on your left handside a Cinema called "Sala Troisi".
Take the first left, the square you see in front of you is Piazza San Francesco D'Assisi.
From the airports:
From Fiumicino, by car take the higway direction of Rome and exit Magliana/Trastevere/Centro, and follow the instructions above.
If you are with public transport take the urban train line FM1 direction Orte, or Fara Sabina, or Stazione Tiburtina.
Get off in Trastevere Station (approx. 25 minutes), cross the Station Square and go on the main road on your left (Circonvallazione Gianicolense). There, take the tramway line number 8 direction city center (Largo Argentina).
Get off in front of the Ministry of Education (Pubblica Istruzione in italian), cross the road opposite to the Ministry and follow the railways turning on your right. The first left is Piazza San Francesco D'Assisi.
From Trastevere Station you can also take a taxi, don't pay more than 5 Euros; it's less than 5 minutes by car!
With the car: take the Grande Raccordo Anulare direction Fiumicino, and follow the instructions above.
With public transport.
Take the coach for the city center, get off at the Terminus (Piazza Venezia/Teatro di Marcello), go back towards the Capitol/Piazza Venezia. On the same handside of the road after few hundred meters there is a big bus stop.
Take number 44 or 75 and get off in front of Sala Troisi Cinema (it is the stop just before the stop in front of the Hospital called Nuovo Regina Margherita). Turn back a few meters and take the first left. The square in front of you is Piazza San Francesco D'Assisi.
Our B&B is just one minute walking from the tramway lines 3 and 8 stops. From Fiumicino Airport or from the new Fiera di Roma (Exibit an Congresses Area) you can get the city train FM1 and get down at Trastevere Railway Station.
The closest underground stop, Piramide, is just 10 minutes walking.