the road begins in salisbury at the castle roundabout and travels north out of the city, passing close to old sarum castle, taking a predominantly straight line to boscombe down and then amesbury before meeting the a303 at countess roundabout where it shares countess services with the major road. at this point it passes within of the world heritage site at stonehenge. continuing north, the road passes near to woodhenge and the ministry of defence royal school of artillery base at larkhill. this part of the route can be hazardous as there are often tanks crossing and the road is susceptible to subsidence. the next significant places are netheravon, and then upavon where the road briefly separates into a one-way system around the village, running concurrently with the a342 to devizes. from here the a345 goes to pewsey, where the pewsey white horse is best viewed, and then continues on to marlborough, ending at a roundabout leading to the high street which is the a4 road.