If you already possess a visa from the US, Canada, Japan, Australia, or New Zealand and are transiting through South Korea, you're eligible for up to 72 hours of tourist activities in the country.

All travelers must present a ticket for their onward journey. This regulation applies at international airports such as Incheon (Seoul), Gimhae (Gyeongsang Province), Yangyang (Gangwon Province), Cheongju (Chungcheongbuk Province), or Muan (Jeollanam). Passengers landing at any of these airports must depart from the same airport or Incheon and Gimpo (Seoul), or Jeju International Airport for their next flight. Upon arrival, passengers must proceed through immigration as usual, presenting their boarding pass, onward flight ticket, and visa from one of the aforementioned countries.
For short layovers where passengers remain in South Korea for a few hours (within the same day) and do not need to claim their luggage, it will be automatically transferred to their next flight. Some airlines in South Korea, such as Korean Air or Asiana Airlines, require approximately 50 minutes for processing, while Vietnam Airlines may take around 70 minutes.
During a layover in Seoul, if you don't have relatives or specific plans, you can join complimentary transit tours organized by the Korea Tourism Organization. These tours typically include a tour guide, transportation, but exclude entrance fees to attractions and lunch.

These tours vary from 1 to 5 hours or allow free exploration of Seoul's capital. With a layover of 1-3 hours, you'll have time to explore the Incheon area, visiting landmarks such as Yonggungsa Temple, Oseong Observatory, Incheon City Museum, Shingi Tourist Cultural Market, and Wolmi Park. If you have approximately 5 hours, guides will take you to Seoul's downtown area, featuring famous sites like Cheonggye Stream, Gyeongbok Palace, Insadong Cultural Street, or you can venture to places you've pre-planned outside the tour's scope.
Arex high-speed train is the quickest way to travel between Incheon Airport and Seoul, taking just 43 minutes each way. The train runs directly, departing every 30 minutes, with a one-way ticket priced at around 8 USD. Recommended route: Airport – Seoul Station – Lotte Department Store – Myeongdong shuttle bus stop – Seoul Station – Airport.
According to Ngôi Sao.
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Reference: Travel guide from Mytour.
MytourJune 18, 2014