Kilsby Tunnel is 2,426yds long and is unusually high at 28ft. Stephenson deliberately made it high to help passengers overcome the fear it was expected they would experience due to the tunnel's length.

The tunnel also has two huge ventilation shafts of 60ft diameter, which can be seen from nearby roads.

Shortly after work began the workers hit quicksand and the tunnel flooded, delaying the railway's completion considerably. Even after a further seven shafts were dug — 18 had been planned — and 13 pumps installed, it took 19mths of pumping to control the water.

George Stephenson assisted.