just go to Korea and feel it yourself - that is the best and quickest way. expensive way though.

I'm in Korea right now, was in Japan and China before I came here. I thought Korea will be a copycat of Japan given all the bashing it has received. I'm surprised at how vastly different it is from Japan. Saying Korea is similar to Japan is like saying Japan is similar to China.
They may all have been similar a thousand years ago but they all branched out quite nicely.

Chopsticks in Korea are longer than in Japan....though shorter than in China. The Koreans do use chopsticks that are thin and metal. They are by far the hardest to learn how to use, but they are more environmentally friendly.
Other factoids:
-Korea has the only scientifically designed writing system. While the word origins are often rooted in chinese, the script is uniquely Korean, created around 500 years ago. It is phonetic (not pictographic like Chinese).
-Korean (spoken) is related to Mongolian in sentence structure (unlike Chinese).
-70% of Korea is mountainous.
-Korea is undoubtedly one of the few places in the world where a mosque (the one in Seoul) sits on top of a hill that is primarily accessible by walking through an alleyway of gay bars and clubs.
-Korea has all four seasons (snicker).

Since the topic is about culturally distinct, here are what you will notice right away:
Restaurants in Korea (Korean restaurants) mostly have low tables where you have to sit on the floor and leave your shoes by the door. Exceptions are fastfoods and restaurants in malls. Every meal will be served with kimchi. Japanese restaurants are expensive. You'll most likely eat in mid-price to low-price range where you'll sit side by side with salarymen. You order by pushing buttons on a vending machine and present the ticket to the server. Conveyor-belt sushi is pretty good too. You'll also encounter standing-only restaurants. All 3 use chopsticks but only in Korea you'll find spoons readily available on the table alongside chopsticks.
Temples are also very distinct. Japanese temples are made entirely of wood. They prefer simplicity. Even the color is brown. Korean temples have elaborate contructions and use plenty of color. Korean pagodas are made of stone which is uniquely Korean. Chinese temples are made of clay and they prefer to color it gold and red. They also use a lot more incense.
If you walk around Akihabara in Tokyo, that's totally uniquely Japanese. You'll be surrounded with manga, the latest consumer electronics, the latest videogames, and the latest elaborate coin-up arcade games. There's also plenty of conveyor-belt sushi place there. Totally different than when you're walking around the Bund/Nathan Rd in Shanghai.
If you visit the war museums on each of these countries, you'll get 3 different interpretations of every conflict they had.

Temples are also very distinct. Japanese temples are made entirely of wood. They prefer simplicity. Even the color is brown
Generally true when speaking about Buddhist temples. But Buddhism is originally an "imported" religion in Japan, although it has been modified after the Japanese adopted it.
However, temples of the indigenously Japanese Shinto religion often have bright, usually bright red (close to dark orange, not sure if there's a separate word for it in English) exteriors.
Maybe my definition of culture is different from yours, but I'm not very convinced by your examples of Akihabara and conveyor-belt sushi. Before any Korean gets angry at me, let me say that I'm not an expert on the history of conveyor-belt sushi, but if I'd have to bet I'd say that that's a Japanese invention. Places where you get a receipt from a vending machine and exchange that for your meal can be found at several places in Japan too.
I'm under the impression that classical Confucian ethics are maintained more conservatively in Korea than in Japan; if there is any truth in that, that probably says more about the cultural differences than manga or pachinko parlours.

It might be easy to compare western countries to give you a reference.
The Japanese are like the British (Island Nation, very proud of itself, very proper, hold on to traditions, reserved)
While the Koreans are more like Italians (Very passionate (just check out world cup 2002 footage, more colourful (koreans swear a whole lot more!!)
There is a Famous Book called "Korea Unmasked" That is written by a Famous Korean Author that outlines this theory. And its a Comic so its a really fun read..
Also I know another Author named PJ ORourke who called the Koreans "The Irish of Asia" and I agree. They are really fun to be around once you get past some of the strange quirks.. They love to drink. Have a very good sense of humor and really let loose.
And Never Ever Compare them to Japan. Especially right now. Koreans are furious that the Japanese Government is claiming The Islets of Dok as there own.
Its korean Territory but the Japanese are playing hardball and really pissing koreans off
here is a site
The Japanese earliest claim to the Island is in 1904 and the earliest Korean one is about 1500 years earlier.. So you do the math..
Anyways... Just trying to give some backstory. I live in Korea so I hear about it alot!
AlsoI find Koreans easier to get to know.
Koreans have a hard outer shell you have to crack, but once you do that they are really true friends.
I have found Japanese harder to really get to know. They are more easy going at first but then sometimes friends will just fade away.

This is my take.
Both Korean and Japanese cultures were heavily influenced by the Chinese culture. I would be believe that Korean culture is more so than the Japanese, which have taken on a life of its own.
In terms of language, the Korean written language used to follow the Chinese system. However, they invented their own some time back to differentiate themselves. If you go to Korea, you can still find old shops or buildings which have Chinese characters. This is especially true for the imperial palaces, with the signages in Chinese. The Japanese Kanji system is inherited from the Chinese. In fact, they preserved some very old letters which is not even in use now in China. The pronunciation of Kanji letters are very similar to the Mandarin pronunciation.
In terms of traditional architecture, both Japanese and Korean are influenced by the Chinese. Especially true for the roofs, one can notice the similarity. However, the Japanese architecture has evolved through the years to take a form of its own. On the other hand, the Korean architectures is still very much like the Chinese due to the proximity. If you visit the Korean imperial palaces, you can see that the architectures are distinctively Chinese.
There are numerous areas which you can notice Chinese influence as well. However, the above two is probably the most obvious, if you have visited China, Japan, and Korea.
Just my 2 cents.
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