The Mary Baker Eddy Library, a research center with two floors of interactive exhibits, aims to explore ideas such as liberty and spirituality through history, with a central role for Mary Baker Eddy, the founder of Christian Science. The most intriguing artifact is the Mapparium [ST], a unique hollow globe 30 feet across. A work of both art and history, it consists of a bronze framework that connects 608 stained-glass panels. Because sound bounces off the nonporous surfaces, the acoustics are as unusual as the aesthetics. As you cross the glass bridge just south of the equator, you'll see the political divisions of the world from 1932 to 1935, when the globe was constructed.