Warning! It only takes one mistake on one day of riding this trail and you could die...
It's a rim trail circumnavigating an old rock quarry with some 20 to 35 foot drop-offs less than a foot from the singletrack path... not for the weak-hearted.
How to get there:
Northeast Mason City... Highway 18 to Kentucky, North on Kentucky, East on 12th, North on Plymouth... about 1 mile up Plymouth road you'll see a pond on each side of the road... park in the gravel pull-off and explore.