The bridge (viaduc) is best approached heading south on the autoroute, you get the most spectacular view of it as it rises towards the south end, and it's on a slight curve too.
Carry on for 15km or so and exit at the next junction, and double back towards Millau. As you reach the town take the road off to the left (towards Albi??), and as you head towards the bridge there's a small turning on the left that climbs up the escarpment to a viewing area.
Then go back down and under the bridge itself there's a visitor centre.
Well worth it!
Oh, and then head off up the Tarn gorge..............................
