Located at Elizabethtown College.
Update: It turns out that there is actually a container near the actual cache that is there for letterboxing. The letterbox is not under the bridge. The cache is in an obvious spot and you will know which one is which. Please do not claim finding the letterbox as a find, it would not make sense. Thanks! This is an easy Cache located near a nature center used by school groups. Location may require shoes that can get muddy. No credit without your signature. Spoiler logs will be deleted. Have fun!