This sets off along farm tracks and country lanes before picking up the Sarn Helen Roman road, a classic route well known to mountain bikers, walkers and motorcyclists alike. The return brings you down a fast tarmac descent and runs along the Senni Valley before rising up 150m again. The final stretch is along Heol Cefn Y Gaer, passing the site of one of the many hill forts in the Brecon Beacons National Park. The descent ends up very close to your staring point.
More information can be found here: http://www.mtbbreconbeacons.co.uk/english_pages/hubs.htm