The second Mourne Skyline Mountain Trail Race on Friday night and Saturday has attracted 300 competitors from 100 countries to the spectacular venue.
The action opens on Friday night with the granite trail 2 miles up hill only race starting on Newcastle Promenade and finishing 1,000 feet above sea level at Millstone Quarry.
Northern Ireland champion Seamus Lynch from Newcastle faces Mont Blanc winner Paul Navesly while World Mountain medallist Sarah McCormack from Ireland defends her title against the in-form Laura Graham.
The race is particularly interesting in that the runners all wear lamps on their head gear to lighten the route.
On Saturday the Garmin Mourne Skyline Race will be held over a 35K course including 3370 metres of ascent with Slieve Donard the final climb before the finish in Donard Park.
Irish Internationals Dan Doherty and Paul Tierney head the line up along with Scottish based Northern Ireland runner Eoin Lennon second last year.
Newcastle pair Iain Bailey and David Steele plus Sam Herron of Mourne will lead the home challenge.
Lizzie Wraith from Team GB will be Womens favourite while Ben Nevis winner Diane Wilson of Dromore a medallist last year will go close as she has been in great form.
Shileen O’Kane, Jacqui Toal and Fran McFadden will place highly along with Hazel McLaughlin.