The workshop venue is June E Huh Center for Mathematical Challenges, located on the 2nd floor of Soo-rim Art Center.

You can show this address to the taxi driver: 

동대문구 홍릉로 118, 수림문화회관
(118 Hongneung-ro, Dongdaemun District, Seoul)

If you take a taxi from the city center of Seoul to Soo-rim Art Center, it should cost around KRW 15,000. 

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 station (Line 6) and Cheongnyang-ri station (Line 1). It will take 13 min. (20 min.) walk from the stations, respectively.