Things to do , see and eat in South Korea

I guess it really depends on what your interests are! Let me know if you want more information on a certain category!

Shopping

• Dongdaemun: they have some cheap to mid-priced stuff here AND a lot of the places are open really late (Doota closes around 4am-5am ish i believe)
• Gangnam: a lot of the areas here have some big name department stores and malls filled with luxury brands. Pretty good if you have a lot of money but if not, it's just nice to walk around in some of these malls to see the "bougie" life
• Namdaemun: CHEAP CHEAP CHEAP! this is a traditional market and there is so much to see, from fashion to household items
• Myeongdong: come here for cosmetics. They have clothing and shoes too but cosmetics reign in this neighborhood

Traditional/History

• Anguk/Insadong: kind of falls under shopping too, they are known for their traditional brushes, papers, etc. also has many traditional tea houses/restaurants and a temple nearby as well!
• Bukchon Hanok Village: traditional Hanok houses; you can take a lot of nice pictures here
• Palaces: Gyeong-bok-gung, Chang-deok-gung, Gyeong-hui-gung, Chang-gyeong-gung, and Deok-su-gung. They all have their own charm and are well worth the visit! 
• DMZ: book a tour to go to the DMZ and see North Korea (kind of)
• Seodaemun Prison: a former prison used by the Japanese to hold Korean independence fighters.  A well-set and thought out museum (but very small; probably only take an hour to see the whole place)
• The War Memorial of Korea: very big and interesting exhibits 

Cool/Interesting Places

• Hongdae: a college town filled with interesting shops, cafes, etc. Recommend going during nighttime to see some busking!
• Mangwondong: Does not seem like much, but if you go inside alleyways with a map, it's an area where you can find a lot of cool restaurants and cafes (not very tourist friendly though... the locals like to do cafe hopping in this area)
• Yeonnamdong: similar to Mangwondong but has become a little more touristy with the "Yeontral park" 

Tourist areas/picture spots

• Seoullo: a nice little "bridge" over Seoul Station, you can take a lot of nice photos here
• Cheonggyecheon: a nice river where you can relax or have a stroll
• Han River: you can ride bikes, leisure sports (although I don't know when they operate esp. since you are going in September....), have a picnic, etc. Just make sure you know which area of Han River you are going because each area has a specific "theme" I guess
• N. Seoul Tower: you can either take the cable car or hike up the mountain, but I recommend hiking one of the trails up there because there are a lot of beautiful sights to see along the way! And the trails are all very easy (some only take 30 minutes to go up)
• Lotte World and Everland: Lotte world is inside the city and Everland is about an hour away. Everland however has more thrill rides whereas Lotte World is very much like Disney World (the experience is what matters)
• Lotte Tower: the tallest skyscaper in South Korea, the views are breathtaking (it will be different than N.Seoul Tower since Lotte Tower is south of the Han River and N.Seoul is in the center of Seoul)

Busan

• Haeundae: probably the most famous beach in Busan. Can get a little tourist-y though
• Dalmaji-gil: a short taxi ride from Haeundae, it's a whole street filled with really nice looking cafes and it has really nice views of the beach (it's on a hill) and it has a nice observation deck where you can see the moon clearly at night (as they say)
• Haedong Yonggungsa: a very beautiful Buddhist temple, it's situated right on the coastline so definitely a must visit!
• Gamcheon Cultural Village: a colorful village filled with art and interesting alleyways (be prepared to walk up some steep roads)
• Taejongdae : a national park and is famous for their rock beach! Has awesome cliffs to look out over the ocean
• Busan City bus tour: definitely a must if you are short on time and want to see a lot

Now, I am missing a lot of other places but, this post is getting too long haha ;) 

P.S. If you can I also recommend visiting Jeju island! It's considered Korea's Hawaii and there's so much to eat and see there!!

I have been there for just a few days in summer 2016 but i still have some things i can recommend~

The Cheongyecheon stream was one of my fave places ever! I was there on a hot summer night and it was so beautiful with the bright moon and the dim lights :D There's nothing much to do there, but it's good to relax and just have a good time
Namsan Tower was also great! Make sure to go on a day when there's not too much pollution in the air tho for a better view~
And since i stayed in Myeongdong i can also recommend to go shopping there~
Hongdae seemed interesting too but we didn't have much time there though..
And if it's still warm enough you can go to the Han river, they had something like a pool(?) where lots of kids played, it was just knee deep and you could walk through or sit on some of the stones in the middle and cool your feet lol

I plan to go back this year and i hope i can visit many more places this time!
I want to see historical places, theme cafes, Jeju, Busan and more but i don't know yet if i can do all these things for the next trip already hahah

There are also a lot of good day trips that can be taken outside of Seoul. The two I would highly recommend are the Garden of the Morning Calm, which is essentially the national botanical garden and is gorgeous, and the Korean Folk Village in Yongin, where you can see how Koreans lived during the Joseon period. Also at the folk village, you can see various traditional forms of Korean entertainment (a 농악 performance, tight-rope walking, horse-riding and archery stunts) and a traditional Korean wedding.

@ftiheart17 I thought so... I afraid by going to Jeju, it will makes me skip many things on Seoul and Busan. Actually I plan to use KTX from seoul to busan. Is it expensive? 

For now I'll put Gyeongju on the list and make time table to see if it fits :D

No wonder you know a lot! Where are you living now?

@tania ktx will probably set you back around 60,000 KRW one way, if you get the regular seat. This compared to about 15,000KRW-20,000KRW on a regular express bus or 30,000 for a comfortable express bus. It is expensive but ktx will get you to Busan in only about 2.5 hours compared to 5 hours on express bus (granted there's no traffic). So if your priority is money, go for the bus but if you're worried about not having enough time, ktx is the way to go!

I used to live in the US, but now I live in good ol' Canada!

Everything depends from where exactly you are going