Pont du Gard is one of the most iconic remains of the Roman period, and I was glad as I finally could tick off this WHS in June 2013. Actually it was my second visit, but I have only sparse memories of a stopover on the way to Spain with my parents when I was a child. At that time access was free and it was possible to walk along the water conduit at the upper level.
Pont du Gard is really impressive, by its height and by its state of preservation. When we stood on the banks of the Gardon, we looked up at the top tier and tried to see the skew of the bridge. But it is not visible, the bridge descends by only 2.5 cm. But you can easily see that the span of the arches varies. And: it's not the bridge on the 5 Euro note. The drawings on the Euro banknotes depict archetypes, not real buildings. Take a 5 Euro note and compare, you will easily notice the major difference: in the real bridge, the piers of the lower and the middle tiers are in line one above another; probably to reduce the load on the arches and to enhance stability. From a shorter distance, you see the protruding stone blocks that were used to fix the scaffolding.
This is certainly a WHS where the weather crucially contributes to the pleasure of the visit. Our visit was on a wonderful sunny day. We climbed the trails on both sides up to all the viewpoints and took photos from almost every angle and distance. For photographers, I would recommend to visit Pont du Gard in the afternoon when the sun shines from south-west on the 'better side' of the bridge (the side without the attached road bridge). We finished our visit with a nice walk through the olive groves back to the parking lot.