Gold

The Spanish didn't steal it all from the Aztecs and Incas (although they tried).  What they missed ended up in some great Gold Museums in Central and South America, and I made it a point of visiting every one - not to mention the more modern offerings in the Middle East.  I even took a tour of a gold mine in South Africa:

U.S., Chile, Colombia, Costa Rica, Egypt, Mexico, Israel, Kuwait, Peru, Qatar, South Africa, United Arab Emirates