The back of the Red Dragon Casino is a location in the casino. This area is where the [ Insert here ] is made. Lee infiltrates this area to find the money plates used to make counterfiet money. Carter’s commotion allows Lee to successfully enter the back. He sneaks in and looks around he stares at a camera for a while. He is then caught on camera by security but Lee fights them and escapes under some bars ( Lee thinks he’s safe behind the bars ) but right after Hu Li appears and puts a grenade in his mouth he then takes him to the upper floor of the casino. It is unknown what this area becomes after the events of the casino but it is likely rebuilt or taken down along with the rest is of casino.
Jackie Chan had a few outtake Bloopers where he both got stuck and fell down trying to slide under the bars.