I was playing ODST the other day, trying to get the 29th audio log on Mombassa Streets. I was near the top of the map when I found an opened security door and walked through it. I walked through a building and ended up outside the map behind the covenant forcefields.
The outside area looked pretty much like the inside, only without any objects or rubbish anywhere, apart from a car and a covenant crate. But I found an odd looking supply cache out there. It had silvery looking doors that looked a lot more durable than the normal supply caches. I spent a good hour trying to figure out how to open the door and exploring Mombassa streets looking for more secret places like that.
Eventually I found the 29th audio log and headed back to the secret area to see if that would open the cache. But the security doors were closed and I couldn't get through.
I haven't tried reseting my campaign progress and I haven't taken a screenshot because the film is like 3 hours long.
So can anyone explain this?