L'Ultrabaie's largest race spans 240 km over five days and five stages around the Baie de Somme, using Saint-Valery-sur-Somme as its primary hub. This predominantly flat running and trail event in Hauts-de-France takes place in early July. Distances range from short 3 km and 5 km options for all participants up to the UB800, which includes approximately 1200 m of elevation gain across the entire 240 km.
The routes connect coastal towns and beaches instead of crossing mountains. Specific legs include Le Crotoy beach to Saint-Valery-sur-Somme for the 14 km, Saint-Valery to Le Hourdel for the 20 km, to Cayeux-sur-Mer for the 34 km, and to Mers-les-Bains for the 70 km. Some races are out-and-back, while others are point-to-point between bay stations. The 70 km also features a relay option. Association Ultrabaie organizes the event, which has capacity for 4000 runners. Participants in the UB14 race can even opt for a short ride on the Baie de Somme railway during registration.