Great Northern operates a train from Stevenage to ExCeL London every 30 minutes. Tickets cost $14 - $21 and the journey takes 25 min.
How to get from Stevenage to ExCeL London
From Stevenage train to King's Cross St. Pancras Underground Station, Tube to Tower Gateway DLR Station, train to Custom House (for ExCel) DLR Station, then walk to ExCeL London. 1 h 7 min £17. From Stevenage taxi to ExCeL London. 53 min £208. From Stevenage drive to ExCeL London. 53 min £9.