By Public Transit: Siam Square can be reached by the Sukhurmit line and Silom Line of the BTS Skytrain system. You can get down to Siam station which is on top of Siam Square.
By Boat:  If you want to reach Siam Square by boat, you can take the Saen Saep Express Boat from Koh San road.
By Bus: Bus 15, Bus 45, Bus 552 can be accessible to reach Siam Square.