Batman Arkham Asylum Ps3 SPECIFIC OF QUESTION 4...?

Where do u find the route into the Arkham mansion? I'm on the part when I walk into the Mansion and it has that security beam going across the Entrence Hall...and it says...LOCATE DR YOUNG...and it says below it...LOCATE A ROUTE INTO THE ARKHAM MANSION...so I know where the Mansion is...but where is the route to get inside it without going across that beam,someone help! Really appreciate it! :D