Where would you suggest adults start to "learn something about the true masterpieces of mathematics"?

I became aware of the following article through Malke Rosenfeld. Thank you!

"With help from professional mathematicians, all of us should make an effort to learn something about the true masterpieces of mathematics, to be able to see big-picture math, the way we see art, literature and other sciences."

http://www.latimes.com/opinion/commentary/la-oe-adv-frenkel-why-study-math-20140302,0,5177338.story?fb_action_ids=622579391123736&fb_action_types=og.likes&fb_ref=s%3DshowShareBarUI%3Ap%3Dfacebook-like&fb_source=aggregation&fb_aggregation_id=288381481237582#axzz2up91g9gM