Plans to transform Norwich Castle Museum and recreate its medieval keep have won £9.2m of lottery funding.
The proposals include reinstating the keep's original Norman floor level. The castle has dominated the city's skyline since it was built in the 12th Century.
The development will also include a new medieval gallery, designed in partnership with the British Museum.
If plans are approved work could start by summer 2019, with the transformed keep due to reopen in 2020.
The scheme is expected to cost about £13m in total. The £9.2m is coming from the National Lottery Heritage fund and the remainder of the money from a mix of public and private sources.
Norwich City Council leader Alan Waters said: "Norwich Castle has long been a cultural jewel in our fine city and one which deserves to be better known.
"This wonderful news will ensure that many hundreds of thousands more visitors will be able to explore and understand one of Europe's most important 12th Century secular buildings in greater depth than ever before."
The redevelopment will also include new visitor facilities such as a cafe and shop and new "digital and learning spaces".
The recreated great hall in King Henry I's castle will be complete with a banqueting table, minstrels' gallery, King's chamber and chapel, according to the museum.
Newly-exposed Norman archaeology and architecture will offer an insight into the castle's past and a viewing platform at battlement level will offer stunning of medieval and present-day Norwich.
Hartwig Fischer, director of the British Museum, said: "This is wonderful news, the Norwich Castle project is exciting and ambitious and will deliver real benefit for the region.
"We are delighted to be working on the project and will lend around 60 important objects for The British Museum Gallery of the Medieval Period which will form part of the new displays in the castle keep."