⛏️ Great County Adit

The Great County Adit, sometimes called the County Adit, or the Great Adit was a system of interconnected adits that helped drain water from the tin and copper mines in the Gwennap area of Cornwall, in the United Kingdom. Construction started in 1748 and it eventually reached a length of over 40 miles (64 km) of a tunnel, providing drainage to over 100 mines at an average depth of 80–100 metres (260–330 ft).