Time Out says
Calling all geography nerds: The Mapparium, the world's largest walk-in globe, is among the city's quirkiest landmarks. Located inside the Mary Baker Eddy Library, it’s essentially a three-story model of the globe built to scale. The perfect sphere runs 30 feet in diameter and can be crossed by means of a glass bridge that bisects its interior. Inside, sound bounces off the globe room's non-porous glass walls, amplifying it ten-fold—which means that whispered sweet nothings from your partner across the room register directly in your ear.
200 Massachusetts Ave
|Cross street:||Clearway St|
|Opening hours:||Sep-May: Tue-Sun 10am-4pm; Jun-Aug: daily 10am-5pm|