Afon Arban? Yes, that is a death march if I recall - starts off OK but gets worse as you become increasingly committed. Also, the bridleway into the forest isn't at all good - not entirely sure it links up with the forest road as I tried (and failed) to find it when planning the Polaris event a few years ago.
For those approaching from the south: 12pm, 30 December 2011, outside the Spar* in Llanwrtyd Wells ready to roll for a 20 mile pootle up to Moel Prysgau, aiming to arrive at around 4pm.
Return to Llanwrtyd the following morning via a different 20 mile route.
* not to be confused with the Spa in Llanwrtyd Wells.
Lots of good trails actually north of Llanwrtyd. I've missed the Real Ale Wobble for the last couple of years, but there's some good forest bridleway and fireroad through Nant-y-cerdin and a good hill top bridleway to Abergwesyn and then fireroad through Nant-yr-hwch to top of the Devil's Staircase. Eye watering descent down the Staircase and fairly straightforward byway/ fireroad up to Moel Prysgau. About 20 miles, bit of climbing but nothing to strenuous. Should have nice views if the weather plays ball.
Return route: exit south from Moel Prysgau, road down to Llyn Brianne then bridleway over to Abergwesyn and (soft option) road to Llanwrtyd or (better option) fireroad into Irfon forest and some more nice bridleway into Nant-y-cerdin and back to Llanwrtyd via off road.