The Semois valley around Bouillon has an excellent network of waymarked walking trails through dense mixed forest — beech, oak, and pine — along both banks of the river. The river's exaggerated meanders mean that short loops can feel much longer, as you repeatedly encounter the same water from different angles. The classic walk follows the south bank east to the Tombeau du Géant (Giant's Grave), a dramatic rocky spur about 3km from town with views over the broadest loop of the Semois.
Trails are well signposted from the town centre. The tourist office provides a free map with several route options ranging from 4km to 15km. Walking here is possible year-round, though the forest is at its best in autumn when the beeches turn. The river is calm enough for kayaking in summer and several outfitters in Bouillon offer rental by the hour or half-day.