Kokoda Loop (purple arrows) 

Crank right off the Shack Track climb on to Lello's Link, then roll 1.9km allong Willow Tree Track (fire road) to the entrance of Shark Attack (at the intersection on your right). With Shark under your belt you have a shorter bail-out option to get you home if the legs are suffering, or hit the testing climb of Reo summit before enjoying the 5km decent of Kokoda. Ride Lello's in reverse then cruise back to the trailhead via Shack Track (following the green arrows). Of course you may choose to divert onto the Diggers Loop at this point; it's only an extra 17km....