Millau Viaduct (Viaduc de Millau)

The Millau Viaduct crosses the valley of the Tarn on the A75 motorway, and at 343 metres, measured to the top of its tallest mast, it is the tallest bridge in the world. That is higher than the Eiffel Tower, and one of its seven piers, the tallest, is higher than any other bridge pier on earth. The bridge is 2,460 metres long and carries the road across on a slender steel deck that seems to float above the cloud when the valley fills with morning mist.

The viaduct was designed by the structural engineer Michel Virlogeux, who has built other long-span bridges in France, and the architect Norman Foster, who gave it its look. Eiffage built it, and the deck was pushed into place from both ends, a method that avoided heavy equipment in the valley. It opened in December 2004, and it closed a gap in the A75, which runs from Clermont-Ferrand south to the Mediterranean near Béziers and had previously been blocked by a long and slow descent through the town of Millau. Today the motorway runs high above the roofs of the town, and traffic that used to jam in the valley in summer now crosses in minutes.

Seeing the bridge is easy because it is visible for kilometres around. The Aire du Viaduc de Millau, a motorway rest area on the plateau north of the valley, has a free exhibition called the Viaduc Expo that explains how the bridge was designed and built, and it has a viewing terrace and shops. A viewing area at the old farm of Brocuéjouls offers another vantage point with information about the countryside and the culture of the plateau. In the town of Millau itself you can look up at the piers from the river banks, and boat trips are available under the bridge. Guided visits are run by the builder's guides and take under an hour, with a modest fee. Because slots fill quickly in summer, book ahead.

The surroundings are as interesting as the bridge. Millau lies at the edge of the Grands Causses, a region of high limestone plateaus cut by canyons, and it is a base for outdoor activities such as paragliding, hang-gliding, canoeing and hiking. The Gorges du Tarn begin nearby and run for dozens of kilometres, and Roquefort, home of the blue cheese, is not far away. The town is also known for its tradition of leather and glove making, and the Marché de Millau is a good place for local food.

The best time to see the bridge is early morning or at sunset, and mist adds drama. It suits engineers, photographers and anyone driving south through France.