The place is unique.
The trains are passing just half a meter over your head! You may seem to be able to reach the trains wheels. The noise and vibrations are scary, but try to stay under the bridge...
The place is rarely empty, so the risk of uncovering the cache is high. To help the cache survive longer, please study the spoiler well and pick the film container in one shot, you may pretend to admire the bridge construction or pose to a photo... I count on your conspiracy imagination!
Small note on cache maintenance: omaggo has volunteered to assist. Thanks!