The Binnian Tunnel was constructed between 1948 and 1952 and is located in the Mourne Mountains in Northern Ireland. The main purpose of the tunnel is to divert water from the Annalong river to the Silent Valley Reservoir underneath a number of mountains including Slieve Binnian, which the tunnel was named after.
A high degree of engineering skills were employed in the building of the tunnel. Two teams of people worked at each end of the tunnel and met in the middle. The tunnel was created using drilling and blasting techniques.
The tunnel was designed to carry 90 million imperial gallons (410,000 m3) of water per day, be 2.5 miles (4.0 km) long, 7 feet (2.1 m) high and 8 feet (2.4 m) wide. When the two teams met in the middle on the 6th December 1950, they were only two inches out.
The tunnel was officially opened in August 1952.