The so-called Tar Tunnel in Ironbridge is a brick-lined tunnel dating from the late 18th century. It was used to extract naturally occurring bitumen which was used to preserve ropes and similar, especially at sea. It is presumed that the bitumen was discovered by accident during canal works or perhaps exploratory trial headings looking for coal seams.
The tar tunnel extends around 900 metres and the first 100 meters cabn be visited as part of the Ironbridge Gorge Museums. Subterranea Britannica visited the full extent of the tunnel by special arrangement. The site forms part of the Ironbridge Gorge World Heritage site.