Architect Bjarke Ingels, who practices what he calls “a pragmatic utopian architecture that steers clear of the petrifying pragmatism of boring boxes,” has created a bold new vision for the Smithsonian Institution. His $2 billion proposal, which has been in the works since 2014, is for the restoration and renovation of the Smithsonian’s iconic campus on Washington, D.C.’s National Mall.

The Smithsonian, the world’s largest museum and research complex, comprises 19 museums and galleries, the National Zoological Park, and nine research centers, and is anchored by the iconic Castle, a Norman-style red sandstone confection that opened in 1855. Ingels’ master plan encompasses a 17-acre site.

For the Smithsonian renovation, the 45-year-old Ingels—whose BIG-Bjarke Ingels Group has offices in Copenhagen, New York, and London— is, according to his project description, striving for “a careful reinterpretation of old and new—finding freedom within the boundaries of strict regulation and historical preservation working with the elements that are already present in the campus.”

Not only does his proposal aim to improve and extend visitor services and create clear entrances and connections between the museums and the gardens, but it also seeks to replace outdated and failing mechanical systems and elements like leaking roofs.

The centerpiece of his plan revolves around the Castle, which has been designated a National Historic Landmark and now serves as a visitor information center and headquarters of the Smithsonian. He envisions restoring its historic Great Hall and adding an underground space for visitor services. The Enid A. Haupt Garden, which his plan calls “a green oasis between the Smithsonian Castle and Independence Avenue,” is another space that he’s “committed to preserving the intimate character of,” according to a statement.

In addition to expanding visitor services, Ingels’ master plan includes new Mall-facing entrances to the National Museum of African Art and the National Museum of Asian Art. He also proposes reconfiguring the Hirshhorn Museum’s sculpture garden by adding two double-height contemporary art galleries and a new auditorium beneath it.

When his original plan was presented, it drew protests from preservationists. Of particular concern was his proposal to address the aging building’s mechanical systems beneath the Haupt Garden, a 4.2-acre green space in front of the Castle that’s designed to look like a richly landscaped 19th-century garden, by adding a glass roof on the Quadrangle Building under it and building a new subterranean auditorium, gallery, cafe, and shop.

Under the revised plan, a new Haupt Garden, which maintains many of the original characteristics, will be moved to the Quadrangle Building’s new roof.

According to Linda St. Thomas, chief spokeswoman for the Smithsonian Institution, the first phase of the South Campus master plan, which will include the Castle, will begin in about three years.