I'll keep it short and to the point for those who are new to South Korea or simply passing through on business - here are the top places to visit in Seoul if you are looking to have some weekend fun (to include finding that special person).
Note: Your best spot for meeting someone may vary based upon your income, age and profession.
Upscale and pricey, it is mostly reserved for businessman who can afford the prices (mostly Korean), beautiful women who have no need to pay, and English teachers who want to pretend for the evening that they can afford the nightly fare. Since the curfew for United States military personnel is 1:00am, it is unlikely you will see many of them once the clubs/bars start to come alive.
Top Clubs - Holic, Eden, Answer, Heaven, Ellui, Phantom with lesser quality clubs like NB catering to the 18-20 something crowd. The list seems to grow longer every few months, as do the venues, so your best bet is to Google them individually and see what events are taking place.
Bar Scene - Timberhouse at the Park Hyatt, Once in a Blue Moon (Jazz Bar), Monkey Beach and Hobar (mostly expats) in Apgujeon, and a smattering of bars in the vicinity of Gangnam Station.
Seedy, fun and less expensive, Itaewon attracts mosty military personnel (before 1am), the standard lot of embassy, businessman, teachers, and Koreans who are western-friendly. Itaewon is better suited for those who prefer a cloistered, inexpensive bar scene, though there are a few small clubs.
Top Clubs - Function, Rococo (http://www.cnngo.com/seoul/play/club-rococo-itaewon), Naked, Helios (after 11pm).
Top Bars - Geckos, All That Jazz, Three Alleys Pub, Scrooges, Helios, Sam Ryan's....in short, there are dozens of bars in Itaewon to frequent. They are all in close proximity to one another, so give them a try and see which one fits for you.
Young and wild, Hongdae surrounds the art school of Hongik University. Lots of unique cafes dot the area, and at night it is home to lots of clubs catering to college students. Inexpensive and crowded it can be overwhelming at times, especially if you are over the age of 30 (some clubs will not allow men in who are over a certain age).
Hongdae attracts lots of foreigners (mostly students and English teachers) and is known as probably the "wildest" place in Seoul.
Top Clubs: Cocoon, M2, NB, Harlem, Club FF (all are very loud, and suited to people in their 20s)
Top Bars: Hobar (there are about 10 of them in Hongdae), Zen Bar, Club FF.
Here is a pretty good article on the Indie Rock scene in Hongdae: http://www.cnngo.com/seoul/play/5-best-indie-rock-bands-hongdae-149011
About a 5 minute taxi ride from Hongdae, Sinchon is better known for its bars. If your looking for a young scene that gravitates toward bars this may be it. Not far from Yonsei and Ehwa, Sinchon is inexpensive, and suited to pretty much everyone - both professors at Yonsei, young businessman, students, etc.
Top Clubs: Bar Fly (this is about the only "club" in Sinchon but it doubles as a bar).
Top Bars: Mike's Cabin, Hobar, Yale Town (great burgers), The Bar, Beer O'Clock, Bar Fly and dozens of Korean bars that you can go to for a relatively quiet drink.
Daehango, or "college street," is located at Hyehwa Station and is great for those who are looking for a more relaxed nightlife. Not nearly as wild as Hongdae, Daehango has plenty of bars, but seems to attract the more tame artists. Numerous theaters and galleries adorn the area (probably more than Hongdae), so this is the place to go if you want to catch the equivalant of an "off-off Broadway" performance and then relax in a bar after the show.
Top Clubs - None that I know of.
Top Bars - All local (the area is fairly centrilized, so if you get off at Hyehwa Station and looks around you are bound to find something good).
Seoul Hotels (Hilton, Walker, Hyatt, Park Hyatt)
All four of these hotels have very nice bars, but the Grand Hyatt is clearly the best. JJ Mahoney's at the Grand Hyatt is a fanastic bar, club, restaurant that is frequented by some of the wealthiest and most beautiful people in Seoul.
Grand Hyatt - JJ's is open until 3am and the crowds can get fairly large on the weekends. JJ's also hosts events on a monthly basis. Prices are steep with nearly all drinks/cocktails in the $15-25 range.
Try this article - http://www.cnngo.com/seoul/play/j-j-mahoneys
Hilton - The Oak Room tends to go quiet by midnight. A small bar it is good for a nightcap.
Park Hyatt - Located near the Coex, the Timberhouse at the Park Hyatt usually attracts a small, but upper class crowd.
W Hotel - The WooBar at the Walker Hotel is second only JJ's - closing around 3am on weekends it sometimes hosts parties and events. Certainly worth a visit if you can afford the expensive drinks.
This run-down is best suited for those who are new to Korea or traveling through. For those who live in Seoul and know it intimately, you may take odds with some of the opinions expressed above. Please feel free to comment on this blog post so we can make the first-time experience for travelers to Seoul even better.
Lonely Traveler Team