I'm interested to hear of reading and listening tangents that people have gone off on while learning Japanese. E.g., has the off-hand mention of some historical figure or (in)famous person's name in a book prompted you to research more about them? What links did you read? What videos did you watch? 

My (most recent) example: In 負け犬の遠吠え, Sakai Junko makes an off-hand reference to 福田和子 (ふくだ　かずこ), a women who spent nearly 15 years on the run from the Japanese police, and was arrested days before the statute of limitations on her crime expired. Searching for information about her led me to this dramatic re-enactment of her 14-year 逃亡. It was quite the escapade. (Warning: Video quality sucks.)

It didn't spawn any huge amount of research but I found it interesting. There was this 天声人語 article, http://www.douban.com/note/263482782/ (the article is really old now, so only Chinese blogs w/ translations have it), that talked about how back during the early Meiji era that because Tokyo was primarily wood buildings and was growing  rapidly, there were a lot of fires. Just like how many arctic natives have many words to describe snow, they apparently had some words to describe different kinds of fires that broke out in Tokyo.

Quote:明治時代に東大で教えた英国人チェンバレンは、日本語には火事をめぐる語彙（ごい）が多いのに驚いた.

(2015-12-17, 9:35 am)vix86 Wrote: It didn't spawn any huge amount of research but I found it interesting. There was this 天声人語 article, http://www.douban.com/note/263482782/ (the article is really old now, so only Chinese blogs w/ translations have it), that talked about how back during the early Meiji era that because Tokyo was primarily wood buildings and was growing  rapidly, there were a lot of fires. Just like how many arctic natives have many words to describe snow, they apparently had some words to describe different kinds of fires that broke out in Tokyo.

Quote:明治時代に東大で教えた英国人チェンバレンは、日本語には火事をめぐる語彙（ごい）が多いのに驚いた.

HINOYOUJIN (火の用心) BEWARE OF (house) FIRES (Kyoto, Japan)

A common sight especially during winter months when the weather is very dry.

There are lots of terminology, search 火＋ことわざ　火＋四字熟語　火＋慣用句

Masako Shirasu: woman of the world
by Roger Pulvers
Special To The Japan Times

Quote:Masako’s sharp eye on the mores of her people can be seen clearly in something she wrote in “Shirasu Masako Jiden”
(“The Autobiography of Masako Shirasu”):

“During the war there was a thing called the tonarigumi (neighborhood association). They would come to the aid of people in need. I didn’t take to this institution. The Japanese may be an honest people, but when they start helping you they also begin to tell you what to do. That’s fine up to a point, but it gradually escalates and they are soon telling you what you have to like and dislike and what you have to do in your daily life. All of a sudden, your clothes are too loud or your manicure too conspicuous. We are still a people like this even though the era has changed.

“The government and the military were overly optimistic and thought you could protect yourself against bombing by passing around buckets and waving broomsticks in the air. When we left the city, the word sokai (evacuation) was not yet in use, and anyone who escaped from Tokyo was labelled a traitor.”

「白洲正子自伝」

Quote:その頃、各町内に「隣組」という組織ができて、お互いに助け合うような仕かけになっていたが、それが私には一番の苦手であった。日本人はよほど正直者なのか、そういう時には必ず世話好きな人たちがいて、指揮をとる。指揮だけならまだしも、だんだんエスカレートして来て、個人の趣味や生活にまで口を出す。きものがはですぎるとか、マニキュアが濃すぎるとか、闇米を食べるとか、・・・・・・しまいには「非国民」呼ばわりをしてヒステリックになる。時代が変わっても、どこにでもいる人種である。

・・・政府も軍部も呑気なもので、バケツのリレーと箒一本で爆弾が防げると信じていたらしい。まだ「疎開」などという言葉は誰も知らなかったし、東京から逃げだすなんて、それこそ非国民の見本のようなものだった。

I don't know if you could call it a rabbit hole in the strictest sense, but I ended up learning a metric-crapton of airship/nautical vocabulary going through the Japanese translation of Kenneth Oppel's "Airborn."

Granted, I'm writing my entire undergraduate thesis on the Japanese translation of the novel, so that's another rabbit hole in and of itself.

A while back I became fascinated by Japanese WWII holdouts and also the Japanese soldier who went native in eastern europe after the war and resurfaced so many years later he was unable to speak japanese.

I forgot about another rabbit hole that I think a lot of people fall into when learning Japanese which is linguistics. If you stick with learning the language long enough, you'll acquire a lot of linguistic terminology you wouldn't otherwise have if you stuck within your native language's family.