Worth doing some reading in advance and making time to do a guided tour of the island and the various stone money locations.

Well, it's maybe not so mysterious as it's been studied quite a bit at this point but it is a must see. The small stone discs are everywhere, even in town, so at first I thought they weren't real. But then we drove around the island(four linked together I believe) and the discs were everywhere. Some were very old, some newer, and we learned how to tell the difference. The village with the most photographed row of discs was somewhat remote and mysterious us because we were the only people there at the time. There is a beautiful Men's ceremonial house nearby on the coast and it is also very beautiful to visit.

I would say that the one thing most people may know about Yap is from history class and the idea of money and how Yap's stone money is an early and unique example of money. Seeing them in person and hearing about the history from a local guide is a historic experience.