You're looking for a bison tube hidden along the bike path. This one might be easy to find, but be careful of muggles when you retrieve it! If you've found either of my caches the Manhan Dossier or the Manhan Hidey-Hole you might have a good idea what to look for. BYOP and please return the cache to its original location hidden in the same way. Happy caching!
Alternate names for this cache (lots of hints here):
Fishing for Bison
Totally Tubular!
Unnecessary Gatekeeping
Bison Tube in a Tube