One Day Itinerary
by DSwede
Many people will recommend a DMZ/JSA tour. It is a unique thing to Seoul, so if that would interest you, look into it. It would take 5~8 hours during the day.
Otherwise, for a one day itinerary, I'd recommend:
Seodaemun Prison History Hall (early morning)
Changdeokgung Palace & the secret garden (late morning)
Insadong neighborhood for handcrafts, art, etc. & for lunch
All of the above are about 5 minutes apart from each other.
Afternoon you could visit the National Museum and/or the folk villages.
A lot of the foreign visitors will visit Itaewon neighborhood for the food options and for cheap shopping. You either like Itaewon or you don't.
Odd Engrish
by Ewingjr98
If you are American, British, Australian, or New Zealanderish? you will be happy to learn that English is used widely throughout Korea. The unfortunate news is much of it is bad English... Usually at small stores and shops, the owners will try to communicate to Westerners or just look cool to Koreans, so they will put English words on their signs. Unfortunately, many of these words come out wrong (like "Chinse Restaurant" instead of "Chinese" or "Cacktail" instead of "Cocktail."
A friend of mine was studying American idioms, like "happy camper" when I glanced at the book and one example it gave was "top quality meat." The example was "that girl has sexy legs. Yeah, she's top quality meat."
In Korean, there is little difference between an "R" and an "L" sound, so it is very common to see and hear words like "Engrish". The English "B", "P", and "V" are also confusing to many Koreans as their sounds are very similar. The pseudonym some American friends of mine used was "Ricky Venus" which many Koreans pronounced as "Licky Pen!s."
Trip planning
by MEdelmann
At least some special tips, made on my own experience: Make exact plans what to do each day. Seoul is a HUGE city and the distances are long. If you visit a special sight , look out if there further sights next to the sight you want to visit .... because it can take a lot of time to reach them.
An example: One day I wanted to visit the Olympic Park. This park is located in the east of Seoul. But I stayed in the west of Seoul, in the Yangcheon district.
It take me more than 2 hours to reach it! I went with subway line No.5 and the train passed around 40 stations. So I decided to visit the Kimchi museum, the COEX Aquarium (they are all in the COEX-Mall) and Lotte World too. You can save much time when planning what to do each day.
Lunar calendar
by asantetravel
The eighth day of the fourth lunar month (this year, May 8th ) is Buddha’s birthday. The streets are decorated with colorful lanterns and there is a parade from the stadium to Jogyesa temple. About 35% of the population in Korea is Christian, so this day is also Parents day. Carnations are the flower of choice as presents. The nights of Seoul are always lit with red neon crosses that top the steeples of most churches!
Religion
by victorwkf
Although Buddhism is still the dominant religion in South Korea, there is the emergence of Christians especially among the younger generation. As such, you will find more and more churches in Seoul with time, like the one shown in the photos taken by me in November 2008.