If, like us, you travel to the Mediterranean, we normally use the old N roads as they are much more scenic than the auto-routes and, of course, are free.
One exception for us is the A75 which is free and runs from Clermont-Ferrand to Beziers in the south. It is one of the most spectacular journeys through the middle of France with ever-changing scenery through the mountains, valleys and flatlands with numerous aires, also with splendid views. One in particular, the aire between J30 & J31 has views of the railway arch, Viaduct de Garabit, built by Gustave Eiffel, it spans the Truyère, near Ruynes-en-Margeride in the Massif Central region, built between 1883 & 1884.

Continue on this journey which then takes you over the Millau viaduct which spans the Tarn gorges. The viaduct does incur a toll, but well worth the fee to observe the splendid architecture and superb views.
There is an aire, on the north end of the viaduct, with a visitor centre explaining the construction of the bridge and an excellent place for taking a break and viewing the bridge.
Want to experience travelling over the bridge, check out the video?    download video

Some facts:
The Millau Viaduct is a cable-stayed bridge that spans the gorge valley of the Tarn near Millau in southern France. In a Franco-British partnership, it was designed by the English architect Lord Norman Foster, (little mentioned) and French structural engineer Michel Virlogeux. As of November 2018, it is the tallest bridge in the world, having a structural height of 343 metres.
Opened: 16 December 2004
Length: 8,071 feet
Width: 105.15 feet
Longest span: 1,122 feet
Clearance below: 885.83 feet