The Mapparium itself is great- but heads up on a few things
A) It's not inside a normal library. Despite the "Mary Baker Eddy Library" this exhibit is basically inside a religious building. Mary Baker Eddy apparently being the founder of Christian Science. The lady at reception WILL assume you are either a) part of Christian Science or b) very willing to learn about Christian Science (from the very biased source of the library about the sect). Both assumptions that made me deeply uncomfortable. I've visited churches that were tourist attractions before, and generally they're much nicer about not assuming your religion or thinking they can impose on you.
B) No pictures are allowed inside the globe, and you can only enter with a guided tour.
Still the price is low, and it's a really neat space.
The tour is more of an audio-visual presentation built into the globe, and is free of any Christian Science talk.
This stained glass globe was built in 1935, and is visually stunning.
One really striking thing was that it hasn't been updated since 1935, and thus has a number of countries on it that don't exist anymore, like european colonies in africa, the USSR, Siam, etc. The proportions of the countries also look a bit different than looking at a globe since you're effectively in the middle of a globe, looking mostly out and up rather than down.
The unique proportions of being inside a globe have unusual effects on the acoustics of the space. There's a whisper gallery effect, and sounds bounce around in unexpected ways. read more