Lincolnshire County Council has £3.5 million to open up the south wall to the public, linking it to the other three walls via a system of cantilevered bridges and timber walkways.
Work is set to begin on the wall, off Drury Lane, in May.
It is part of a wider regeneration and repair project and creating the complete circuit of the walls will need further work in 2012 and 2013.
Visitors currently enter Lucy Tower – the medieval castle keep used as a graveyard for executed prisoners in the 19th century – via steps in the six o’clock position.
The aim is to open a blocked up doorway on the west side of the tower – discovered by archaeologists – for access.
Once inside the tower, people would exit via the existing doorway and follow a new walkway around the exterior tower wall to get back on to the south wall at the nine o’clock position.