Not super challenging, but when your tired...
http://youtu.be/1mwbUGDDEB4
The technical difficulty is about a 3(maybe), 'till you pick up some steam, then the deadheads, rocks, stumps, & potential fall over the side starkly remind you to keep your feet on the pegs and bike on the trail.
http://youtu.be/YegTrsBLFko