The River Doubs, which forms part of the Swiss–French border, widens out at the peaceful village of Les Brenets, 15km southwest of La Chaux-de-Fonds. It takes a little over an hour to walk from the village along Lac des Brenets to the Saut du Doubs (no vehicular access), a splendid crashing waterfall where the river cascades 27m into a natural pool. If walking poses challenges, boats operated by Navigation sur le Lac des Brenets will get you there.
Le Locle–Les Brenets trains (Sfr3.60, seven minutes) are frequent.