From the South/Centre
Via Milan: Follow the “tangenziale est”, the east side of the motorway bypass around Milan into the direction of Vimercate, until to its end at Usmate.
From the West
Via Milan:Coming along the motorway Milano-Varese, once in Milan, take the motorway Milano-Venezia (Venice) into the direction of Venice until the exit Sesto San Giovanni. Now follow the signs for Lecco, go onto the road SS 36 Milano-Lecco-Colico, and from Colico the SS 38 in the direction of Morbegno-Sondrio-Tirano up to Bormio.
From the East
Via Brescia: Coming along the motorway Venezia-Milano, exit at a Brescia Ovest (Brescia West). Follow the Brescia bypass into the direction of the Lake d’Iseo until it ends and then take the road SS 510 into the direction Iseo-Boario-Darfo. Go on taking the road SS 42 into the direction Edolo. Once you reach Edolo, take a turn for the road SS 39 into the direction of Aprica, crossing the Aprica pass. You will reach Tirano, then follow the road SS 38 for Bormio. The Aprica Pass (1176 m) is open all year round.
From the North
Via Switzerland passing through Chiavenna: Maloja Pass 1815 m which is open all year round.
Via Switzerland passing by Tirano:Bernina Pass 2323 m, open all year round
Via Switzerland passing through Alta Valtellina (Livigno) Coming from Zernez in the Swiss Engadin go through the Tunnel Passo del Gallo (Galleria della Drossa), open all year round, during the daytime only:Tuesday to Sunday: from 8.00 am to 8.00 pm - Monday: from 5.00 am to 8.00 pm - Pay toll (Please note: They do not take credit cards only Euro's or Swiss Francs).

BY TRAIN

From Milan Central Station, direct trains to Tirano (Sondrio).
Bormio is 41 kms covered by regular bus from Tirano railway station

useful link

TRENITALIA

MAPPA PER RAGGIUNGERE LA VALTELLINA