The flamboyant, arching and gravel-strewn Iron Bridge, which gives the area its name, was built to flaunt the new technology invented by the pioneering Darby family. At the time of its construction in 1779, nobody could believe that anything so large – it weighs 384 tonnes – could be built from cast iron without collapsing under its own weight. There's a small exhibition on the bridge's history at the former toll house.