Brecon Blue route is quite a challenge but does allow for numerous possibilities of short cuts. Look out for walkers on the narrow rocky descent down to the Neuadd, Cwmcamlais.
The climb to the top of Cefn Llechid rewards you with a pleasant descent through bracken covering open hillside. Once you pass through Defynnog you have a pleasant jaunt through the Senni Valley following farm tracks and country lanes. You then have to climb 150m to the Sarn Helen Roman road, which takes you back to the Centre.
More information can be found here: http://www.mtbbreconbeacons.co.uk/english_pages/hubs.htm