Bangkok has finally opened its Airport Link from the city of Bangkok to its international airport, Suvarnabhumi. To access the Airport Link you need to jump on the MRT which connects to the airport line. The train takes apprx 25 minutes from Siam. As of writing Bangkok Airport Link is only opened between 7 am until 10 am and 16:15 pm until 10 pm. Closed saturday, sunday and public holidays. The ticket is free during the current test period.
City Line commuter trips, with set fares at Bt15-Bt45, take 30 minutes to reach the airport, departing from Phaya Thai, Ratchaprarop, Makkasan, Asoke, Ramkhamhaeng, Hua Mak, Ban Thap Chang, and Lat Krabang stations, and will end at the last stop of Suvarnabhumi.
Below you find a picture gallery describing each stage of the journey from Siam station.