I'm not exactly sure what you're talking about cuz i haven't played it and you haven't given a lot of details but i've did some research and this is all i could find about secret stuff on metropolis
"Go through the window the two giant Tyhrranoids appeared in and you can use the Hypershot to swing across to the other side and pick up a Titanium Bolt. Use the Hypershot to swing back to the room.
In this room is also the Teleporter to the Insomniac Museum. It is outside the window on the right, but it is only active between 3:00AM and 4:00AM. (Hey, they aren't called Insomniac for nothing). You can however set your PS2 clock to a time between 3:00AM and 4:00AM and use the Teleporter to enter the Insomniac Museum."