Blisworth Tunnel has no tow path inside, but is wide enough for two narrowboats to pass in opposite directions. Work began in 1793, but errors by contractor left a wiggle in the tunnel, and after three years work it collapsed due to quicksand, claiming the lives of 14 men. It was then decided to begin again with a new tunnel. By the time the rest of the Grand Junction Canal had opened between London and Braunston, Northamptonshire in 1800, apart from the crossing of the River Great Ouse, the section of canal from Blisworth to the lower end of Stoke Bruerne locks
Shrewley Tunnel which crosses the tunnel; having crossed this the path then descends on another ramp to reach the southern portal. The interior of the tunnel is unusually wet and this has led to the creation of flowstone formations. The tunnel runs from the south-east to the north-west. From the northern portal, the canal is level for to the bottom of a flight of five locks at Knowle, which raise the level of the canal by . Kingswood Junction, which connects to the Stratford-upon-Avon Canal occurs about halfway along this stretch. To the south, the canal if level for around to Hatton