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After watching weather forcasts for the weekend decided on a late sunday start as forcast gave a decent window from sunday afternoon until monday night.
http://www.netweather.tv website was bang on, had light showers for first 3 hours but from 4pm on sunday cloud started to lift and from 5pm had clear skys throughout.
Day one
Started about 12.30 Sunday 3/10/2010 at Capel-Y-ffin follow signs for "Grange Trekking", turn left up to Grange then right to end of lane then turn left up the hillside, footpaths more like stream beds after mornings torrential rain but hoping forcast was right, thought go for it anyway. Follow path diagnally left up hill to top of ridge by a large Cairn 1.9 km.
Should now have views down to Grwyne Fawr Reservoir and up to Pen y Gadair Fawr. At this point you could head SE to the top of Chwaral y Fan @ 679 metres, but as I knew i was limited for daylight I continued over ridge south towards Mynydd Due Forest, Enter forest via small gate the follow forest paths generally down hill to join small road at gr so251 286. Go left down road for a few metres to find footbridge over Grwyne Fawr 1.9km.
Cross bridge and turn right along forest track for a few metres then take small path steeply uphill through forest, Keep heading up through forest, crossing two forest tracks and when you reach the top forest track(woodland felled on far side of track) turn right walk along track to gate onto hillside. Bear west up hill for about 0.45 km to top of Pen y Gadair Fawr @ 800 metres 2.4 km. Light rain now stopped, weather now just cloud comming and going. From here head NW for 1.8 km to the top of Waun Fach @ 813 metres 1.9km.
Follow ridge generally NW for about 3.2 km, cloud lifted well above tops by now. Then head NE for 1.2 km to trig point @ 713 metres, continue along ridge for 1.6 km to gr so 220 345 then turn SE down valley for 1.6 km on eastern side of Nant Bwch to great Bivi Site.
Day two
After a wonderful clear night woke up to blue skys headed back up valley then turned NE to top of the Twmpa @ 690 metres 2.1km.
Then head east down a well made path to Gospel Pass 1.2 km, then NE up to trigpoint on Hay Bluff 1.8km. Starting SE follow Offas Dyke path for 5.5km passing over the Black Mountain @703 metres, continue passing over the 637 metre point at gr so 267 322 just past this point is another set of slabs with a small cairn by the end of it with a small path going right (IGNORE THIS PATH) continue for 300 metres where footpath from Olchan Valley to Capel-Y-Ffin crosses Offas Dyke path and turn right onto this path. Follow this path downhill (path very muddy, steep and slippy in places) until you reach a farm track, just to the left you will see the footpath continues down to a footbridge over the Afon Honddu, once over bridge bear right to style and onto the road, once on the road turn right to head back to Capel-Y-Ffin.
All in all a great walk with a perfect bivi spot.