At the Mapparium at the Mary Baker Eddy Library, 200 Massachusetts Avenue, (888) 222-3711, www.marybakereddylibrary.org, visitors traverse a 30-foot glass bridge, surrounded by hundreds of brightly colored glass panels depicting the world as it was in 1935.

Children can stand on one side while parents whisper from the other, and you will all learn how sound travels inside a glass sphere. Admission $5, students $3, younger than 6 free. Closed Monday.