Montalcino is part of the provincia of Siena. You can get there without a car by using the bus service that leaves from the Siena train station , number 114, or in several places along the utside walls. One of the best places to get it is at the base of the moving staircase that goes to and from Piazza San Francesco, at the end of via dei Rossi. Or Porta Pispini, or Porta Romana. Get your ticket before from a tobacchaio, as they never have them on the bus. The bus also stops at Buon Convento, where the trains also go, both from Siena and Grosseto your connection to Roma.
You can enter the city through its orginal fortified wall in several places.Be prepared to walk up a steep incline, unless you use the threee moving staircases, one near Porta Ovile, that goes to San Francesco and via dei Rossi, one near Porta Fontebranda that goes near Piazza San Giovanni, near the Campo, and a third that leaves from the Train Station and goes to the entrance at via Camollia.