The autostrada A12 takes you along the Tuscany coast to Carrara. When you exit the autostrada, it's a simple matter of following the initial sign to Carrara and then following the "cave di marmo" or marble caves signs. You'll go through Carrara, then start to climb the slopes of the Apuan Alps or Alpi Apuane. You will be heading toward the town of Colonatta and the Fantiscritti marble quarry where Michelangelo selected much of his marble. Along the way there will be several souvenir shops selling all manner of marble and granite objects; even the smallest of these can be quite heavy.
Remember that once you get into the mountains you're sharing these small roads and tunnels with huge marble-moving machinery. It's not dangerous if you're paying attention while driving and exiting your car.
From their vantage point on the autostrada many folks make the mistake of wondering why there's snow on the mountains in August. That's not snow, it's exposed marble and the marble dust and tailings that result from the quarrying of the blocks.