You can learn more about your desitnation at http://www.historicbridges.org/bridges/browser/?bridgebrowser=iowa/pavenue/. Note that you will travel a few miles of gravel roads, at least, to get here. As indicated above, do NOT attempt to reach this location if there is flooding along the Iowa River. A young man tried to cross the swollen river here in 2013 and had to be rescued from the flood waters.
Most of the other, more colorful stories of this area are from the distant past. Many were shared with me by my father who grew up in southern Tama County and hunted and fished throughout the Iowa River basin in this region. The most colorful story was of a 1920s circus train which derailed near here on CNW (at mp127.75). The story suggestes that a few circus animals survived the crash and escaped, while others including elephants and a giraffe were killed and buried nearby.
The cache you seek is magnetic and about the size of a deck of playing cards. BYOP. There is room for one or two very small trading items and you do not have to "go below" to find the cache.