This is the Stoumont blue route of 14 km and 543 m accent/decent. There are currently (Nov 2021) 11 similar Routes listed in the ExtraTrail system, which are all referenced on fastestknowntime.com, including the 30 km Stoumont Black Route.
13,7 kms; 543 m elevation gain
ExtraTrail is a network of trails in the Ardennes in Eastern Wallonia, Belgium, specifically designed for trail and ultra run training. The routes are designed in circles from 7 villages (easy access by car or public transport) each having 4 routes of different length and elevation (green, blue, red and black). Due to the landscape all the trails have significant ascent/descent and very technical stretches, ideal for training. The loops are also interconnected to form a network with possibility to design longer circles or A to B routes. In fact, the 158 km UTDS is designed by combining all of the 7 villages using this network. All black courses of ExtraTrail are above 30 km and have more than 750 m accent, which makes them tough and slow.
Link to ExtraTrail: https://extratrail.com/en/