When High Street (aka South Willingham) Tunnel was planned, its length was 255 yards and there were no refuges. The latter was an oversight on the part of a designer which was later rectified with three refuges being cut. The length more than doubled to 557 yards.
The tunnel's construction was difficult and its opening delayed. A goods train first passed through it in September 1875 - three years after work had started. Passenger services began more than a year later when the full 21-mile line was completed.
Landslips were common around South Willingham. In 1939, a major one blocked several yards of line close to the tunnel's eastern entrance. Calamity was averted thanks to an eagle-eyed passer-by who rang the local signalbox to get trains stopped.
Armaments were transported along the line during the Second World War. One important bombing raid on Germany had to be cancelled because the engine bringing the armaments was too big to fit through the bore. It should have been changed at Lincoln.
Passengers services were withdrawn in 1951 but goods continued to be carried until 1st December 1958.
Today the tunnel is a bat hibernaculum and the site is designated as an SSSI.