The Smithsonian Institution announced a major overhaul of its museums in Washington along the south side of the National Mall that could cost $2 billion before completion by 2036.
The focal point of the project is a "revitalization" of the mid-19th century iconic Smithsonian Castle that will include shops, cafes and the restoration of its Great Hall.
Other facets of the project include an expansion of the Hirshhorn contemporary art museum, underground and overground links between museums, and major building repairs.
The so-called Master Plan, drawn up by the Danish international architectural firm Bjarke Ingels Group, is subject to approval by the National Capital Planning Commission, a federal agency.
"The proposed Master Plan will be implemented over a 10-to-20-year period beginning in 2016," the Smithsonian said in a statement that estimated the total cost at $2 billion.
Funding would come from public and private sources, it said.