Dinant's tourist season runs from Easter to October, with the peak in July and August when the boats, kayaks, and citadel cable car are all running and the riverbank fills with day-trippers from Brussels. May, June, and September are the sweet spot — everything is open, the weather is reliable, and the crowds are bearable.
Winter is quiet. The caves, kayaks, and most boat trips close from November to March, and the town shuts down considerably. The citadel and the church stay open year-round, and the famous International Regatta of Bathtubs — a chaotic August race down the Meuse in homemade craft — is the calendar event most worth timing a visit around.