Not sure if decade, as I don't have good memory for such stuff (sorry!), but certainly at least for last year, the following book that had a really huge impact on me:

Gai-Jin by James Clavell

It showed me how different cultures can have very different "codes", how they can see others as "barbarians" purely based on that; more specifically, helped me look more critically on (part of) European culture and history through "foregin eyes", and better understand some aspects of Japanese culture taking them nearly all the way from "weird" to "natural". While at the same time being just a super entertaining and engrossing story!