The Doors of Arkham Asylum
Arkham's large, wooden Manor Doors flew open when a Batman reappeared in Gotham. The Entrance Hall has been split into two down the middle: One way in, one way out.
Security is rather meticulous around the entrance (like that helps, it's Arkham). Contraband and weapons are confiscated and visitors are given ID badges to help them travel through the Asylum.
