In the center of the science center lies an open-air shaft. You can’t get in through the outside, but it is easily accessible from within the building.
The shaft lies next to a little-used stairwell, which leads to a door without a handle by Lawn Avenue.
The only way into the stairwell is via the shaft. The best way to do this is to ride the elevators to a floor, any floor, and wander around until you find the door to a grated-in alcove. Each alcove has two doors; The other leads to the stairwell.
This stairwell has the interesting distinction of being heavily graffitied–But mostly with chalk. If you go to the bottom of the shaft via the 2nd floor, you can find chalk scattered on the ground.