Base
They weren’t able to see any other doorway that led into this room, which only led them to believe that their only way out was back the way they came. But how were people getting in and out of this room in the first place? They had to crawl through the archway and walk past the giant as they did.
The room was clearly some type of secret lab or base and it was operated by the government. Although the police officers were authority figures, they knew that this was way above their pay grade. They were going to have to get out of there before special agents showed up to catch them.