There are so many various activities to do 24/7 around Seoul. The city is full of energy at night, where most shopping centers and markets are open until midnight. Every experience is very convenient and enjoyable.

Amusement parks
Lotte World, [9]. (Metro Line 2, Jamsil stn) One of the world's largest indoor amusement parks that is located in Seoul by the Jamsil Station. It has a folk museum where one can have an insight into ancient Korean life. Lots of rides, and reopened in the summer of 2007 after a massive reconstruction.
Everland, [10]. The Korean version of Disneyland. It is south of Seoul and transportation by bus is the easiest way to get there. Non-stop buses to Everland leave from various parts of Seoul daily. Has a miniature zoo where one can see a lion-tiger hybrid.
Seoul Land [11]. Theme park located in Gwacheon. This park was opened just before the Olympics in 1988. It is easy to get to by subway and is open year round.
Children's Grand Park, Neung-dong, Gwangjin-gu,[12]. The park was constructed after the decision of the City Planning Facility in 1971 and was opened on May 5, 1973. The park has a zoo, amusement facilities and restaurants. To get there, simply take the subway to Children's Grand Park on line 7. Avoid the weekends as it can get very crowded.
Gambling
Horse Racing, Seoul Racetrack in Gwacheon. Races are normally only held during weekends, night racing also takes place during August. During the week, visitors can take guided tours of the grounds.
Seven Luck Casino, [13]. Two locations in Seoul: Gangnam, attached to the Grand Intercontinental Hotel, and the Millennium Seoul Hilton Hotel in central Seoul. The casinos are only accessible to foreigners (it is illegal for Korean citizens to gamble), so remember to bring your passport. Various card tables and slots are available to play. There is a bar and cafe that serve food and drinks, although expensive.
Skiing
There is a free shuttle bus starting at 8:10AM from somewhere along Jong-ro (road) that takes you up into the mountain to the Bearstown resort (South Korea, Gyeonggi-do, Pocheon-si, Naechon-myeon, Sohak-ri, 295). Ask you local touist information where the bus stop is exactly. Prices: ₩52,000 half-day skipass, ₩69,000 full-day skipass, ₩22,000 ski or snowboard rent, ₩20,000 cloths rent - however, you will get the equipment and cloths much cheaper at shops further down from the lift station next to the bus carpark, but you need to walk there (300m / 10min).
The shuttle bus back leaves at 5PM. Don't be too late! The bus leaves from the lower bus parking area, not from car park where you where dropped off - it's a 10-15 minutes walk there from the lift station. Some information: [14]
Mountain Biking
Korea MTB Adventures, 205-402 Samsung Remian Apt, Goyang-si (line 3 Wondang Stn), [15], ☎+82 10 7417 1457, (info@koreamtbadventures.com). This company rents mountain bikes, offers guiding services, and supplies equipment such as helmets, gloves, hydration packs, shoes and light systems. They offer half day (3-4 hours - ₩100,000 or $90US with bike and gear) and full day (4-6 hours - KRW150,000 or $135US with bike and gear) tours in a few locations in and around Seoul. Options include downhill riding at Namhansanseong, cross country riding near Goyang, and urban riding through downtown Seoul.
Performing Arts
Sejong Center for Performing Arts, 81-3 Sejongno, Jongno-gu, (line 5 Gwanghwamun Stn),[16]. Oldest and one of the largest multi-purpose theatre in downtown Seoul and home of Seoul Philharmonic. Biggest pipe organ in East Asia is in its Great Auditorium, and several video art pieces from Nam June Paik are in the entrance of auditorium.
Seoul Art Center, 700 Seocho-dong, Gangnam-gu, (line 3 Nambu Bus Terminal stn), [17]. Another great place for performing arts and Korean traditional art.
KBS Hall, (line 9 National Assembly stn). Home of KBS Philharmonic Orchestra and KBS Traditional Music Orchestra.
'LG Arts Center, 679 Yeoksam, 1 Dong Kangnum gu, Seoul, (Metro line #2, Yeoksam Station, Exit 7), [18] ☎+82 2 2005 0114.Modern, multi-purpose performing arts auditorium opened in 2000, features live musical, theatre and dance performances from Korea and worldwide. Visit website for performance schedule and ticket information. Underground parking is available.
Spas, saunas, and massage rooms
Saunas generally take the form of public baths in Korea, and are a popular form of relaxation. Services such as hair cuts and shoe cleaning are generally available. Some saunas also include sleeping areas for overnight stay. These are known as 찜질방, or jimjilbang, and can be a cheap alternative to hotels when you're just passing through an area.
Dragon Hill Spa, 40-713, Hangangno 3(sam)-ga, Yongsan-gu, Seoul, ☎ +82 2-792-0001, [19]. This is a typical jjimjilbang with a lot of additional facilities for entertainment and amusement. It can be very packed sometimes. ₩13,000/12h overnight, else ₩11,000.
The Spa Grand Hyatt Seoul, Grand Hyatt Seoul Hotel, 747-7 Hannam 2-Dong, Yongsan-Ku, ☎ +82 2 797 1234 (info.grandhyattseoul@hyattintl.com), [20].
Park Club Spa & Fitness Centre, Park Hyatt Seoul Hotel, 995-14 Daechi 3-dong Gangnam-gu, ☎ +82 2 2016 1234 (seoul.park@hyattintl.com), [21].
JES Massage Center at Incheon Airport, Seoul Incheon International Airport, 2 locations: Passenger Terminal 4th Floor Rest & Relax Zone & Concourse A, ☎ +82 32 743 6925.

You will visit the following 3 places:

Gwacheon-si

Seoul

Seoul, officially the Seoul Special City, is the capital and largest city of South Korea. A megacity with a population of over 10 million, it is one of the largest cities in the world. The Seoul National Capital Area is the world's second largest metropolitan area with over 24.5 million inhabitants, which includes the Incheon metropolis and most of Gyeonggi province. Almost half of South Korea's population live in the Seoul National Capital Area, and nearly a quarter in Seoul itself, making it the country's foremost economic, political, and cultural center.

Gangnam-Gu