## Barrage du Gouffre d’Enfer, Planfoy (Loire): history-rich dam, dramatic gorge, and big-view hiking

Location: Brg du Gouffre d’Enfer, 42660 Planfoy, France (45.3929079, 4.4459224)
Type: masonry arch-gravity dam on the Furan, in the Pilat Regional Natural Park, near Saint-Étienne.

### Why this spot matters
Completed under Napoleon III (works 1862–1866; commissioned 1870), Barrage du Gouffre d’Enfer was among Europe’s first masonry arch-gravity dams and, at ~53 m high, the tallest in France—and the world—at the time. Built to supply drinking water, regulate summer low flows powering local mills, and protect Saint-Étienne from floods, it’s a rare blend of industrial heritage and wild scenery.

Since 2003, the reservoir has been kept empty most of the time: the dam now primarily serves flood control (and as backup when the newer upstream Barrage du Pas-du-Riot is low). If you’re expecting a full lake year-round, that detail is crucial.

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## Quick facts (verified)

– River: Furan (a tributary coursing through Saint-Étienne).
– Design & era: arch-gravity masonry; conceived by engineers Graëff, de Montgolfier, Conte-Grandchamp during the Second Empire.
– Dimensions: ~53 m tall, ~102 m crest length (selected specs).
– Current purpose: flood attenuation; historical water supply role now secondary to Pas-du-Riot upstream.

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## What to do there

### 1) Follow historic trails to the dam wall and belvédère
Tourism was built into the project from the start: a path carved into bedrock leads to the foot of the dam, with a belvédère viewpoint and interpretation along the way—unusually forward-thinking for the 1860s. Expect rock steps, railings in key spots, and gorge views that explain the site’s name (“Gouffre d’Enfer” references the dramatic chasm). Hors-Cadre

Hiker intel: Several signed loops in the area link Gouffre d’Enfer with Pas-du-Riot; difficulty ranges from moderate family walks to long, steep circuits. A representative loop from Planfoy (≈8.7 km / 800 ft gain; “intermediate”) showcases both dams and forest ridgelines. Always check route notes and seasonal advisories before committing.

For a longer challenge, the Pas du Riot – Gouffre d’Enfer circuit is listed as “hard” (≈18 km / ~660 m gain) on AllTrails—plan 5.5–6.5 hours and bring mountain-path footing.

### 2) Try the Via Ferrata (with kid-friendly and adult lines)
Directly opposite the dam wall you’ll find the Via Ferrata de Planfoy – Gouffre d’Enfer, a well-equipped route network with two graded lines: an easier PD (often used for children/initiations) and a D line for adults, plus a 10-meter suspended bridge and varied rock passages. Proper ferrata kit and know-how—or a guide—are non-negotiable. Ferrata France

### 3) Rock climbing on Roche Corbière
The tooth-like Roche Corbière spur near the gorge is a historic climbing sector (documented locally since the 19th century) with numerous routes across grades and aspects. If you climb, consult a current topo and local guidance for bolt status and access.

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## Planning your visit

### Best time & what to expect
– Scenery: Granite walls, the stark curve of the dam, and a gorge with cascades. Because the reservoir is often empty, the experience is about engineering and canyon scenery rather than a lakeside ambiance.
– Seasonality: Trails are year-round (weather-dependent). Surfaces can be slick in winter or after rain. Via ferrata and climbing depend on conditions; check local notices in advance. Ferrata France
– Family notes: Short approaches and interpretive signage suit mixed groups; reserve the long loops and ferrata “D” line for fit, experienced parties.

### Safety & access
– Footing: Expect rock steps, steep sections, and railings; wear grippy footwear. Hors-Cadre
– Ferrata: Helmet, harness, certified lanyards, and route knowledge required. Guided outings are widely available in the region if you’re new to ferrata. Ferrata France
– Climbing/canyoning: Check updated topos and local regulations; water levels and access can change. The nearby Cascade en Gouffre d’Enfer area sees canyoning—access and flow are variable. waterfalls

### Inclusivity & practicalities
– Trail inclusivity: The gorge paths feature stairs and uneven ground; wheelchair access is limited on the historic sections carved in rock. When planning for mobility needs, focus on belvédère viewpoints reachable from roadway pull-outs and shorter, smoother trailheads around Planfoy—consult local tourist offices for the latest accessible options. (The official Saint-Étienne tourism board offers current on-site guidance and an interpretation trail.) Hors-Cadre

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## Context: a paired system with Pas-du-Riot
Gouffre d’Enfer quickly proved undersized for a fast-growing industrial city in the late 1800s, so Saint-Étienne built Barrage du Pas-du-Riot upstream (1877). Today, Pas-du-Riot handles primary storage; Gouffre d’Enfer mainly shaves flood peaks and occasionally supports supply when needed—explaining the routinely empty basin you may see at the older dam.

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## Responsible visit tips
– Stay on signed routes to protect fragile gorge vegetation and avoid rockfall zones below the wall. Hors-Cadre
– Check route status (Komoot/AllTrails/local board) the week you hike; storm damage sometimes closes sections or alters grades.
– Carry layers and water—shade in the chasm can make temperatures swing. General visitor reports mention alpine-feel shade and slickness in cold snaps; kit up accordingly. Local

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## What’s near the dam (for a fuller day)
– Planfoy village & forest ridges: Scenic loops link viewpoints above the Furan.
– Saint-Étienne (city museums & industrial heritage): Pair engineering history at the dam with design/industry sites in town. (City attractions vary; verify opening times close to your visit.) — general context, check the local board for specifics. Hors-Cadre

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## What’s potentially outdated or variable
– Water level / “lake” appearance: The post-2003 operating mode means the basin is often dry; any photos online showing a full impoundment may not reflect current reality.
– Ferrata details and access notes: Grades are stable (PD and D lines), but gear rules, seasonal restrictions, and minor re-routes can change—consult current route pages or the Planfoy site before you go. Ferrata France
– Trail conditions: Online distances/elevation may differ by variant; cross-check a recent GPX.

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### Coordinates & mapping
– Main viewpoint / dam area: 45.3929079, 4.4459224 (Planfoy, Loire).

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### Bottom line
Come for the Second-Empire engineering and gorge drama, stay for the ridgeline walks, belvédère views, and the via ferrata directly facing the dam. If you expect a shimmering reservoir, adjust that mental image—the site’s value today is the cliff-and-canyon landscape wrapped around one of France’s formative waterworks.

Sources cross-checked for accuracy as of November 2025; verify ferrata/trail status shortly before your hike.