The Smithsonian has unveiled plans to give museums and gardens along the south side of Washington’s National Mall a $2billion face-lift, creating more welcoming entrances, improving connections between museums and refurbishing the iconic Smithsonian Castle. At the plan’s heart are improvements to the first Smithsonian building, the Smithsonian Castle, which opened in 1855. The plan calls for the Castle to get two new underground levels. And two other museums would get entrances closer to the National Mall. The plan was designed by the Copenhagen- and New York-based Bjarke Ingels Group.