Korea

The peninsula is divided into two countries:

• North Korea (Democratic People's Republic of Korea or DPRK - 조선민주주의인민공화국, 朝鮮民主主義人民共和國)
• South Korea (Republic of Korea or ROK - 대한민국, 大韓民國)

Both countries regard the Korean peninsula as one country that is awaiting reunification, divided by the Korean Demilitarized Zone (DMZ)
The shared border village of Panmunjeom in the middle of the DMZ can be considered as part of both North and South.
South Korea also includes many island territories, notably Jeju island to the south, Hongdo to the West, and with Ulleungdo and Dokdo to the east.

• Pyongyang (Korean: 평양시) – Capital city of North Korea
• (Korean: 개성시) – Former capital in the Goryeo era, now an industrial development zone in North Korea with South Korean participation
• Wonsan (Korean: 원산시) – Port city on the east coast of North Korea
• (Korean: 서울) – Capital city of South Korea
• Busan (Korean: 부산, 釜山) – Largest port and second largest city of South Korea
• (Korean: 인천, 仁川) – Large port city near Seoul in South Korea
• Daegu (Korean: 대구, 大邱) – Third largest city in South Korea

• The truce village of (Korean: 판문점) in the middle of the Korean DMZ, and shared territory of both Koreas
• Jeju (Korean: 제주도) island is the favorite domestic tourist destination for South Koreans
• (Korean: 경주) was the capital if the Shilla kingdom, and is full of history
• Ulleungdo (Korean: 울릉도) and (Liancourt Rocks) (Korean: 독도) islands are a remote spot in the East Sea
• The Baekdu Mountains (Korean: 백두산맥) on the border of North Korea and China have special significance for all Koreans

Itineraries

• - along the east coast of Korea, both North and South

The Korean nation is called Hanguk (한국, 韓國) in South Korea and Chosŏn (조선, 朝鮮) in North Korea.
Historically Korea was divided between various kingdoms and at its height the northernmost Goguryeo kingdom reached into much of what is now north-eastern China. Later the unified country fixed its borders approximately where the present North Korean border lies against China and Russia.
The Korean nation was occupied and annexed by Japan from 1910 until the end of the second world war in 1945. Shortly thereafter it was divided by the allied forces and a devastating civil war, called the Korean War began in 1950 that ended three years later. Since then it has remained divided into the communist North with a hereditary dictatorship and a capitalist — and since the 1980s, democratic — South.
The two countries have been in a state of 'cease fire' for the past 60 years; however, the relationship has always been strained and risk of another devastating war is always a possibility.
The people of Korea are known as Koreans, and are ethnically homogeneous throughout the peninsula. There are no other ethnic groups historically associated with living here, although more recent times have seen immigration into South Korea from China and South East Asia. Ethnic Korean communities can also be found in neighbouring China, whose border area with North Korea, Yanbian in particular, is home to the largest Korean population outside Korea.
Although culturally both countries share the same heritage, the different paths both have taken in the past 50 years mean that you have to refer to the Wikivoyage pages for South Korea and North Korea to gain a relevant understanding.
There are not many practical examples of the Korean nation as a concept. The two Koreas occasionally team up together at the Olympics under a unified flag, and there is a joint industrial zone in the North Korean city of Kaesong. South Korea regards all citizens of North Korea as Korean citizens with a right to live in South Korea (as North Korea does with citizens of South Korea), which incidentally is almost identical to the way West Germany treated East German citizens that reached its territory.

The language of Korea is Korean. Since the division of the country into two very different states after the Korean War, differences in language between north and south have increased, with South Korea importing many English words into its vocabulary due to American influences. In addition, it's rare that people from the North and South have the opportunity to interact. Nevertheless, the language is still very much mutually intelligible between Korean speakers.
South Korea has been a strong ally of the United States since the Korean war, and the US variety of English as a second language is highly promoted and a key requirement for everyone in the education system. That said, English proficiency in the general South Korean population tends to be poor, though people who deal with foreigners regularly will be able to speak English. Japanese and Mandarin are also spoken by many in the tourism industry.
North Korea will, unfortunately, present you with few chances to speak to North Koreans. Typically your guides will be English speakers (or upon request speakers of other "world languages"), although most of the general population may have learned either Russian or Mandarin Chinese.

Entering North Korea is relatively difficult, and as a rule can only be done via a state sanctioned tour group from Beijing. Typically flying from Beijing to the capital Pyongyang is the most common method, although potentially road or rail crossings across the border are possible.
Entering South Korea is relatively easy for most nationalities and can be done most commonly by air globally, or by sea from Japan, Russia and China.
It is worth noting that there are no practical options for directly travelling between the two Koreas. If you are in South Korea then you will typically first need to travel to Beijing and then take a direct flight to Pyongyang in North Korea. Also note that it is criminally subject to up to ten years in prison under the National Security Act (국가보안법) of South Korea for its citizens to travel to North Korea without the prior permission of the South Korean Ministry of Unification (통일부).
There used to be tours of North Korean tourist spots from South Korea — for example, the Mount Kumgang Tourist Region — but they have since been discontinued and are unlikely to resume any time soon.

There are no (realistic) travel options directly between North Korea and South Korea. The only place you can actually cross the border between the Koreas are inside the peace conference rooms in Panmunjeom that are bisected by the border. There you are not allowed to exit the room through the "wrong" door to the other side.
North Korea has extremely heavy restrictions on personal and group travel. Expect only to travel as part of a state-sanctioned tour with a highly prescribed itinerary.
South Korea has many options for travelling around the country, with an extensive and modern air, train (including high speed rail) and road network. Outside of the DMZ border area there are generally no restrictions on travel outside military areas.

• Visit the 'last frontier of the cold war' in the Korean DMZ.
• Sites from the kingdoms making up Pre-modern Korea can be seen both in the North and the South.

• Visit a traditional Korean sauna/bath house (jjimjilbang)
• Go skiing in the former Winter Olympic resort of Pyeongchang, location of the Winter Olympics in 2018. North Korea also has a ski resort for foreigners called Masik near Wonsan

A spicy fermented cabbage dish known as kimchi (김치) is shared by both Koreas.
Slightly sweet rice cakes (떡, 糕 'duk') are popular, served in multiple colors as a desert, or in thick spicy sauce as a common street food.

A liquor called Soju is the shared drink of both Koreas.

Refer to the North Korea page for details on the unique safety issues of the North. Suffice to say that you have zero risk from crime with a real risk of offending the authorities and suffering consequences if you do so. Otherwise it will be hard for you to get into trouble since everything is so carefully planned out for you.
Refer to the South Korea page for safety issues in the South. South Korea is an advanced country with a very low crime rate.
The safety issue shared by both Koreas is the risk of war between them. Again, refer to the relevant country you are visiting in order to understand this better.

Most tourist journeys for westerners to North Korea are guided tours starting by air from Beijing and returning there as well. You are unlikely to get any other options, although in theory (in practice it is difficult for westerners) you could take the train to Russia's far east as well as take a train between Beijing and Pyongyang.
From South Korea you can continue your journey to Japan, China or Russia by air or sea.