Culture: I mentioned cooking because it’s one of the things I enjoy the most, and it gives you a rather good grasp on a culture. Which ingredients do they use? Are dishes typically made for small or large groups? Are techniques intended for everyday cooking, or for more laborious festive events? What about culinary influences? etc.

Depending on where you live, if there’s a Japanese descendants community, odds are they celebrate some festivals, and they’re often open for outsiders. It’s a great way to interact directly with some of that culture.

That said, textbook history helps a lot. As well as Wikipedia; sometimes you learn a lot by stumbling upon some page about lacquer pictures, pottery repair or even cherry trees. It’s all about how you “parse” it together.