Smithsonian internships offer an incredible range of learning opportunities. Because each unit of the Smithsonian (Natural History Museum, Smithsonian Libraries, American Art Museum, etc) understands the learning opportunities it can offer best, each unit manages their own internship application process directly.
A number of Museum related summer opportunities have an approaching March 1 deadline, including the National Museum of African Art, National Museum of American History, National Portrait Gallery, and Smithsonian American Art Museum.
A annualized list of Smithsonian deadlines can be found here: https://www.smithsonianofi.com/blog/2012/12/26/smithsonian-internships/
with more information on current available opportunities here: https://www.smithsonianofi.com/internship-opportunities/