A cast iron arch bridge over the Grand Union Canal.
Can be muggly around here.
Tweezers and pen required.
NB: The cache could no longer be attached at the original location, so it is now approximately 20m from the coords - magnetic, beneath the bridge. New hint.
Haqre oevqtr, zntargvp, oruvaq J.Evpuneqf & Fba.