Work on Norwich Castle first began just after the 1066 Norman Conquest when 98 Saxon homes were demolished to create a huge man-made fortified mound.
The castle dominated the countryside for miles around as a royal palace, then as a prison and later a museum.
Norfolk County Council is to select a contractor to restore the castle to its former glory at a meeting on 10 June.
The council wants to open up the stone castle’s keep „from basement to battlements” to uncover its lost secrets.
Image copyright Evelyn Simak Image caption The castle stands on a huge man-made mound in Norwich city centre on the site of 98 demolished Saxon homes
Excavations of earthworks under the keep have already shed light on the medieval diet and way of life of the castle’s residents.
Boreholes have penetrated to a layer of dark soil which may be the level of the Saxon homes.
Image copyright Norfolk Museums Service Image caption New exhibition space is being planned for the museum Image copyright David P Howard Image caption The keep already has a museum and art gallery but more levels are to be introduced
Margaret Dewsbury, cabinet member for communities and partnerships, said: „Once complete, it will be the most accessible grade one-listed medieval castle in Europe, boosting the county’s economy with 300,000 visitors per year.”
The Norwich Castle: Gateway to Medieval England project will recreate the 12th Century Norman royal palace, create a British Museum gallery looking at the medieval period, an early-years learning facility and provide a rooftop viewing platform.
About £8.7m of the funding comes from the National Lottery with the rest coming from the council (£2.2m), and the rest from trusts, foundations, central government and private companies, organisations and individuals.
„Visitors will see the sights and hear the sounds of Norwich Castle during its heyday as a royal palace,” a council spokesman said.