There are 2 riddler trophies in there going by the trophy map and the entrance is locked and the exit isn't a door you can interact with and I can't seem to find any vents or anything. I'm missing some thing but where?
If you haven't progressed far enough in the story, it is locked. You'll go in eventually --- "You wrote that the world doesn't need a savior, but everyday I hear people crying for one." - Superman Returns
You get in through a sidequest. Look for one called Bird in the western section on the north side of the bridge. --- "To roll poorly once may be regarded as misfortune. To roll poorly TWICE looks like carelessness." 3DS Friend Code: Micah 4682-8451-8168