More runners than ever before - almost 2,000 - will be taking part in this year's Snowdonia Marathon which has been described as Europe's toughest race.
The race is one of the most spectacular events on the athletics calendar and S4C viewers will be able to join in the excitement in Marathon Eryri.
Morgan Jones will present the programme with Nic Parry and Dafydd Whiteside Thomas commentating.
Snowdon is a stunning backdrop to the marathon which begins in Nant Peris and circles the foothills of Wales and England's highest mountain before finishing in the village of Llanberis.
Starting from Nant Peris at 300 feet, the route heads up to Pen-y-Pass at 1100 feet before winding down the Nant Gwynant Pass to Beddgelert and turning off to Waunfawr along the Cwellyn Valley. Then comes the sting in the tail - the grind up to Bwlch y Groes at 1200 feet before dropping down to the finishing line at Llanberis.
Production company Cwmni Da has followed a cross-section of runners in their race preparations and the programme will be profiling them.
The runners include marketing officer Carys Roberts of Llangrannog, who has previously completed the Dublin Marathon, and a sheet metal worker from Cwmgors, Amman Valley, Geraint Smith, who took up running after retiring from rugby. Also featured are the Dolgellau-based runners' club, Rhedwyr Meirionnydd, and husband and wife, Gareth and Jen Jones, who train and run on their farm at Llanwenog near Llanybydder.
The programme will also feature pictures and emails sent in by other runners and will show how money raised last year by the race's committee helped build two climbing walls at a Snowdonia primary school, Ysgol Gynradd Dolbadarn.
© 2010 S4C
O Gymru / Made in Wales