Mary Baker Eddy was a convention-breaking 19th-century thinker and founder of Christian Science, and her eponymous library presents exhibits on her influential work. The institution also includes exhibitions on the impact of The Christian Science Monitor, and curious visitors can explore the Publishing House Lobby, where printing equipment was once housed.
Though entry is complimentary, you need to purchase admission—and hop on a tour—if you want to visit the Mapparium. Tours run every 20 minutes, and tour entry is first–come, first–served. Since you can get free entry with a Go Boston Pass, it's easy to pair your library visit with stops at area attractions that offer complimentary Go Boston Pass admission, like the must-see Museum of Fine Arts.