Transportation (from Incheon Airport):

Address: 
Old Add : 2F 101-16 Itaewon-dong Yongsan-gu Seoul (서울시 용산구 이태원동 101-16번지 2층)
New Add : 2F 30 Noksapyeong-daero 26na-gil, Yongsan-gu, Seoul (서울시 용산구 녹사평대로 26나길 30번지 2층) 

Airport Limousine Bus (6030): 
Bus Number 6030 - Fare :15,000Won/person - Destination: Hamilton Hotel, Itaewon
http://www.airportlimousine.co.kr/eng/lbr/lbr02_1.php#6030

Subway:
(i) 4,000Won/person,   Incheon Airport(AREX Express Train) -> Gongdeok Station (Transfer to line 6 subway) - Itaewon Station( Exit 4)
      
(ii) 4,000Won/person,   Incheon Airport(AREX Express Train) - Seoul Station - Bus 421 to Hamilton Hotel

Taxi: 
60,000 won