This page provides some brief summaries on traveling to IBS, Daejeon from Incheon International Airport (ICN). You can find more detailed descriptions in the link below.
https://www.ibs.re.kr/eng/sub01_08_01.do
Option A. Direct Airport Limousine bus to Daejeon → IBS
1. (Terminal 1) Go to 1F exit No. 11 / (Terminal 2) Go to B1 bus stop No. 5
2. You can find a ticket box near the bus stop. Buy tickets for 'Daejeon'. If you use a ticket vending machine, select 'Chungcheong'→'Daejeon'.
3. Get off at Daejeon Government Complex(Daejeon-cheongsa)
4. Take a taxi and tell the driver you are heading to Institutes for Basic Science (IBS).
You can show the taxi driver below. (Korean address)
기초과학연구원으로 가주세요.
유성구 엑스포로 55 기초과학연구원
*First Bus - 6:20 (T1) 6:00 (T2) / Last Bus - 22:50 (T1) 22:30 (T2)
*Bus timetable: https://www.airport.kr/ap/en/tpt/busRouteList.do
(click 'Chungcheong' and go to 'Daejeon' tab)
*Bus Fare: 26,300 KRW
*Bus stop locations
Option B. Airport Limousine bus to Seoul Station → KTX Train to Daejeon → IBS
1-a. Take bus 6001 (17,000 KRW)
(Terminal 1) Go to 1F exit No. 5 / (Terminal 2) Go to B1 bus stop No. 29
1-b. Take bus 6702 (18,000 KRW)
(Terminal 1) Go to 1F exit No. 3 / (Terminal 2) Go to B1 bus stop No. 18
2. Get off at 'Seoul Station'.
3. Take KTX train to Daejeon. (~24,000 KRW)
Online ticket purchase: https://www.letskorail.com/ebizbf/EbizbfForeign_pr16100.do?gubun=1
4. Get off at 'Daejeon' station.
5. Take a taxi and tell the driver you are heading to Institutes for Basic Science (IBS).
Option C. AREX train to Seoul Station → KTX Train to Daejeon → IBS
1. Take AREX train (subway) to Seoul Station. You can choose Non-stop(express) or All Stop.
(Terminal 1) Across the street from Terminal 1 exits / (Terminal 2) Go to B1
2. Take KTX train tickets to Daejeon. (~24,000 KRW).
3. Get off at 'Daejeon' station.
4. Take a taxi and tell the driver you are heading to Institutes for Basic Science (IBS).
*subway station location
Terminal 1 1F 
Terminal 2 B1
