You are allowed to enter the Fermilab site by presenting a valid, government-issued picture ID to the guard. Only the driver is required to have this ID. They will ask you where you are going, to which you reply, “Saturday Morning Physics”.
You may ride a bicycle to SMP, if you like. The guard will ask for your ID, so be sure to have one! There is bicycle parking on the east side of Wilson Hall, approximately underneath where the word “Hall” ends on this map.