A 100 km (62 mile) circular ultramarathon starting and finishing in Chesham, Buckinghamshire, with approximately 1,800 m of ascent. The route explores the Chiltern Hills Area of Outstanding Natural Beauty using woodland trails, chalk paths, bridleways and rural tracks. Elevation is accumulated through repeated climbs across rolling terrain rather than sustained mountain ascents. Underfoot conditions vary between firm trail, dirt path and chalk surfaces that can become slippery when wet. Course marking, navigation approach and aid station locations are defined by the organiser’s official event information.