The workshop venue is at Building 1 (제1호관), Korea Institute for Advanced Study. (Google map)
The invited talks will take place at room #1501, located on the 5th floor.
You can show this address to a taxi driver:
서울시 동대문구 회기로 85, 고등과학원
(85 Hoegi-ro, Dongdaemun District, Seoul)
There are two bus stops shown in the picture on the right. After passing through the main entrance of the campus, climb up the stairs. You will be able to locate Building 1 on the left.
If you take a taxi from the city center of Seoul to KIAS, it should cost around KRW 15,000.
For public transportation, you can purchase Tmoney card from almost any convenience store in South Korea.
Alternatively, you can add Tmoney card from Apple Wallet in your iPhone or Apple Watch.
If the bus line 201 / 273 / 1226 / 3216 passes nearby your place, you can also come by bus. Google maps works well for public transportation.
If you take a subway ride, the nearest subway stations are Korea University (고려대학교) station (Line 6 - Brown line) and Cheongnyang-ri (청량리) station (Line 1 - Dark blue line). It will take 13 min. (20 min.) walk from the stations, respectively.
Seoul has two main airports - Incheon international airport (ICN) and Gimpo international airport (GMP).
Most flights from outside Asia land at Incheon airport.
There is an airport railway (AREX) that connects both airports to the city center (Seoul station). You can take either the direct one (costs 11,000 KRW) or the all-stop one (costs 4,750 KRW). The bus line 201 connects Seoul station to KIAS. Alternatively, you can ride subway line 1 from Seoul station to Chengnyang-ri (청량리) station and then take bus line 201/3216.
There are airport limousines connecting each airport to several corners of Seoul. You might prefer this on your way to your hotel, especially if it is not near the city center.