Have you ever stood on a bridge a long train is going under? The sheer mass of the vehicle passing beneath you is a bit awe-inspiring.
The cache should be an easy find, a small micro in an easy to reach spot. But it's not a park and grab. Park on either side of the bridge (or even down at the high school if you want a longer stroll) and walk up to the top of the bridge to retrieve.
(This is the second of ten caches we're placing to celebrate 1000 finds.)