Here are a few suggestions for day walks:
Park at SO052172 (below Torpantau). Take the rough path heading NE across the boggy slope. Cross the stream and join the Beacons Way for a while up Craig y Fan Ddu. Continue along Craig Fan Las to SO055203. Turn sharp left and follow the escarpment traversing Fan Big, Cribyn, Pen y Fan, Corn Du. From Corn Du continue along the escarpment SW at first then SE to SO019182 descend the gully. Follow the path to the little reservoir and across the dam. Follow the track to the end of the public road and then cut through Taf Fechan forest, the walk up the road back to your vehicle.
Park in Llanfrynach, walk up the lane and then the track that passes just left of the summit of Bryn and continue until you reach the escarpment. Follow the escarpment over Fan Big and Crybyn until you get to Pen y Fan. Reverse direction back to when you are just beginning to walk up Cribyn again. Take the path that cuts across the NNW face and walk down Bryn Teg. Follow footpaths and a little bit of lane back to the village.
Park near Glyntawe and take the track that starts with a steep zig-zag and continues NW over Banwen Gwyn. Continue to Esgair Ddu, then head NE to Waun Lefrith. Follow the escarpment back to Glyntawe.
Park in Llanbedr (SO229203). Take the track that heads steeply E down to the river and then the path roughly N up the far side until you are overlooking Hen Blant. Turn left and follow the track that passes a little left of Crug Mawr. Continue following the track along the line of hills until you get to Waun Fach. Squelch across the morass and turn left to Pen Trumau and follow the line of hills southward to Pen Cerrig-catch. Descend to the dip before Table Mountain, head left and follow the path to Gelli fanw.
If you are with the very young, lazy, or infirm you could park at the Gospel Pass SO236350. You can follow the escarpment either way from there with minimal effort. The area below to the N has lots of places where families park and picnic. Or if you are a bookworm you could waste a few hours in Hay on Wye. Or you could have supper there and drive up to the Gospel Pass again and camp on top of Twmpa.
If is it tipping down with rain and you can't face climbing a mountain the waterfalls at Ystradvelte are a nice alternative.
Edited: 19/04/2013 at 17:13