32.5
PDI
15.3 mi
DISTANCE
5,241 ft
GAINED
6.5 %
AVG. GRADE
FULL CLIMB STATS
Page Contributor(s): Ard Oostra, Montreux, Switzerland
INTRO
Barrage de la Grande Dixence climbs 15.3 miles and 5,241 feet from Sion, the biggest city in Valais, up the Val d'Herens to the base of the Grande Dixence dam - the tallest gravity dam in the world at 285 meters. At the top, the dam holds back Lac des Dix, the largest lake above 2,000 meters anywhere in the Alps.
This is a climb built around one enormous landmark. The road itself is a steady, well-paved ascent through the villages of Vex and Heremence, with views that open up dramatically in the final miles as the dam wall comes into sight - a sheer concrete face rising almost 300 meters straight out of the valley floor, dwarfing the cars parked at its base.
The Val d'Herens has seen real geological activity in recent years - a rockfall closed the access road for about a month in summer 2025, and a debris flow shut it again briefly in late June 2026 - so it's worth checking current road status before you go, even though the road has reopened both times. Much of the water behind this dam is actually pumped uphill from Lac de Cleuson, a smaller reservoir in the neighboring valley to the west that's also the finish of a separate PJAMM climb starting from this same Sion hub.
PLAN YOUR ROUTE
We've partnered with Sherpa-Map.com to bring you the best route planning tool. With a PRO Membership you can use this climb as a reference when creating your route. Barrage de la Grande Dixence gains 5,241 feet over 15.3 miles at a 6.5% average grade - a long, steady effort rather than a spiky one. The lower miles out of Sion warm up gradually before the road settles into the Val d'Herens and holds a consistent 6-7% grade nearly the whole way to the dam.
The steepest riding comes in short bursts near the top, where the road switchbacks up the final approach to the dam wall - the steepest quarter-mile reaches 11.1% - but there's no single brutal pitch that defines the climb the way there is on steeper Valais neighbors like Croix de Coeur. This is a climb that rewards pacing over raw power.
Roadway: The road is paved the entire way to the dam and is generally in good condition, though this valley has seen real disruption in recent years - a rockfall near the site's cable car closed the road for about a month in summer 2025, and a debris flow at Combe de Bajin cut the road again in late June 2026, reopening July 3, 2026. Check Heremence's tourism site or the cantonal road-status page before you go, since this is a genuine recurring risk in this valley rather than a one-off.
Traffic: Traffic is light to moderate - this is a dead-end road serving only the dam and a handful of alpine hamlets, not a through route, so there's no pass-through traffic. Expect more cars on summer weekends when day-trippers visit the dam and its viewing terrace.
Parking: Free parking is available at the base of the dam itself, at the end of the climb. Sion, at the start, has ample parking near its train station if you're arriving by car or combining this with a rental-bike trip from the city.
Sion has every service you'd need - bike shops, grocery stores, cafes - so there's no reason to carry much beyond normal ride food from the start. Heremence, about two-thirds of the way up, has a small selection of shops and cafes if you need a top-off before the road empties out above town.
There's also a cafe right at the dam's base, plus a smaller one at the top of the dam wall reachable by the site's cable car, if you want a proper break before heading back down. The dam sits above 2,100m, noticeably cooler and windier than Sion at 500m, so pack a layer for that final stretch and the ride back down.
Before heading out on any cycling adventure check out our Things to Bring on a Cycling Trip and use our interactive check list to ensure you don't forget anything.
Sion is the biggest city in Valais and a genuinely useful base for a multi-day cycling trip - it has its own train station with connections across the canton, a historic old town beneath two hilltop castles (Valere and Tourbillon), and enough restaurants and lodging to make it worth a night rather than just a pass-through.
The dam itself is worth the trip on its own merits - a cable car climbs the dam face to a viewing terrace in about five minutes, and the site includes a small museum on the dam's construction, guided tours inside the wall, and even a zipline for anyone looking for more than a photo stop. This climb and Lac de Cleuson, in the neighboring valley to the west, both start from this same Sion hub and feed the same hydro system - riders based here for a few days can combine the two without changing hotels; see our Routes in the Area tool for other climbs nearby.
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