There are literally hundred's of fantastic walks in the Brecon Beacons but few would argue against, that the 4 waterfalls walk is up there with the best.
A pleasant 30 minute drive from The Draen and you are very close to waterfall heaven, featuring 4 x outstanding waterfalls, one of which you can walk behind, this makes for a great day out.
Not far from these falls, is Henrhyd Falls which featured in the film Batman, as his bat cave, well worth a visit.