There is not much time left to enter the 10th Anniversary Active Northumberland Kielder Marathon Weekend! The event takes place from 12th - 13t h October, with entries closing on 11th October, but with the Half Marathon already sold out and the 10K run nearly full, now is the time to make sure you don’t miss out! Known as Britain’s most beautiful marathon, the Kielder Marathon follows an almost completely off-road track and is celebrating its tenth year this year.