The Smithsonian Institution's Castle on the National Mall in Washington, DC The Smithsonian Institution has scaled back its $2bn plan for expanding buildings on the southern end of its Washington, DC, campus, while unveiling details of the restoration and renovation of its 1855 Castle and its 1881 Arts and Industries Building (AIB). The updated cost has not been disclosed. Presenting the second stage of the revised programme on Wednesday to community leaders, a Smithsonian historic preservation specialist, Carly Bond, focussed on the Castle and AIB as well as an underground utility plant that will serve those two buildings and others. The Castle, an administrative building, and the AIB, a former exhibition space that has been mostly closed since 2004, are both National Historic Landmarks.