The Smithsonian Released a $2 billion plan that would reinvent the area surrounding the iconic Smithsonian Castle by creating new entrances and connecting underground galleries in what has been described as the biggest project considered for the National Mall in Washington, D.C., in more than a century.

Designed by architect Bjarke Ingels, the proposal calls for renovations to the red-stone Smithsonian administration building, known as the Castle, and the addition of two underground levels of visitor amenities, including a cafe, a store, an auditorium and restrooms. The new spaces would connect to the S. Dillon Ripley Center, the Arthur M. Sackler Gallery and the National Museum of African Art, which currently have below-ground entrances. The design would replace the pavilions with glass-walled entries visible from the Mall and rising from the corners of the Castle’s Enid A. Haupt Garden.

Also, the now-empty Arts and Industries Building would undergo renovations to house the proposed Smithsonian American Latino Museum, which awaits congressional action. The proposal still must be approved by The National Capital Planning Commission and the Commission of Fine Arts. Construction is not expected to begin for another five to seven years and could take as long as 20 years to complete.