Into the pressure chamber, I dare say not. I heard a rumour that it's possible but I haven't seen any evidence of it. There are a few manholes around the soccer field which may enter around the chamber but inside I didn't see much. The usual access is locked of course, and the area is littered with cameras. Also, the control room has a bank of security camera monitors, which seem to be fairly well watched from our observations. 2am might be a different story. Lastly, would you risk being deported when you can simply take the free tour? I can only imagine the probing you'd get for being caught inside - especially when you've no ability to convey that you're just an exploring photographer!