Great County Adit

The Great County Adit is an extensive underground tunnel network beneath Cornwall that served as a drainage system for dozens of mining operations. This intricate web of passages connected multiple mines and channeled water that accumulated during their daily work.

The system began in 1748 as a solution to a major problem facing mines: water seeping into underground workings. Over time, more mine owners connected their operations to it, transforming it into a massive infrastructure undertaking.

The tunnel system reflects how mining communities in Cornwall worked together to solve a shared problem through engineering innovation. Visitors walking through the region can still see remnants of this collective effort in the landscape and architecture.

Water still flows through the old passages today and exits the system near Twelveheads, where it discharges into a river. Visitors can observe the lasting impact of this ancient drainage system by visiting the portal and surrounding landscape.

The system achieved its massive capacity not through one central installation but through hundreds of steam engines scattered across the region. This distributed approach allowed smaller mines to also benefit from the drainage technology.

Location: Cornwall

GPS coordinates: 50.23440,-5.14000

Latest update: December 12, 2025 09:01