Stwlan Dam Bike Climb - PJAMM Cycling

1.8 mi
909 ft
9.9 %


Page Contributor(s): Nathan Allen, Wales


This bike climb along a service road to Stwlan Dam is an incredible, must-do climb.  Those who have done this climb invariably refer to it with great admiration: "amazing climb," "awesome climb," "stunning" and so on.  This is also a brute of a climb, ranked #10 in Wales.  There are few climbs that are on both the Top 10 Epic and Top 10 Hardest hill climbs, and this one deservedly serves both lists. 

Visit our Top UK and also our Top Wales hill climbs pages for photos, summaries and statistics for their respective top hill climbs.  For the Top 10 Most Epic climbs, visit our Wales Most Epic and our UK Most Epic pages. 
9.9% average grade gaining 277 meters in 2.8 kilometers with 0 descent.  Other than 400 meters at 2.5% in the middle of the climb, this is a beast with 67% at grade 10-15%.  The steepest 500 meters averages 12.1%.  

See more details and tools regarding this climb's grade via the “Profile Tool” button.
Roadway:  Great condition - very narrow service road.

Traffic:  Walkers/hikers and cyclists and a rare service vehicle. 

Parking:  If you drove to Tanygrisiau to do this climb (it would be worth the drive!), park on the side of the road 60 meters from the start of the climb (MapStreet View). 
Provisions:  At the Lakeside Café 600 meters south of the start of the climb (MapGoogle Map + Reviews).  
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.
Use the “Routes in Area” button on the menu bar to see other bike climbs in this area. 

Consider visiting the Zip World Slate Caverns while in the area, 3.8 km north (Map;  Google Map + Reviews). 



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view of one-lane roadway surrounded by green pastureland and rocky hillside, huge dam in middle background

Cycling the incomparable Stwlan Dam, Wales

Ride 1.8 miles gaining 916’ at 10% average grade.

photo collage includes aerial drone view of roadway and dam

We asked Simon Warren to provide us with lists of the Top 10 Hardest and Top 10 Most Epic bike climbs in England, Wales, Scotland, and the UK.  Simon ranked Stwlan Dam as the most epic bike climb in Wales and #2 in the UK, just behind Scotland’s epic climb, Bealach-Na-Ba. We relied heavily on Simon Warren’s Top UK Climbs Series in ranking and documenting UK bike climbs ( - they are the Gold Standard for cycling climbing in the UK.

climb start, eastern edge of Tanygrisiau, bike parked in front of metal gate, one lane roadway

Start the climb at the eastern edge of Tanygrisiau by riding up a roadway free of motor vehicles.

Climb summary by PJAMM’s Brad Butterfield:

If Bwlch y Groes is the Crown Jewel of Wales, then Stwlan Dam is Crown Pearl…hm I’m not sure that analogy makes much sense - but you get the point. There is a gate at the bottom of the climb with a gate for hikers to walk through. Unless you’re really good at Tetris, you’ll need to lift your bike over the fence; the gate is a bit tight to fit a bike through.

climb start, large skree pile near roadway

Giant skree pile to our right just after beginning the climb.

photo collage shows Tanygrisiau Reservoir

Tanygrisiau Reservoir at our backs as we climb.

Of course, your sheep friends will keep you company throughout the winding climb, but you most likely won’t see anybody else. Massive, imposing boulders line the roadway and the impressive dam is in sight for the last third of the climb. Switchbacks take you up the the dam, and if you're so inclined, hop the gate and ride across the actual dam for some unforgettable views of the road below and the lake held hostage by this remarkable cement engineering project.

photo collage show sheep along hillside, dam in background

What’s a climb in Wales without sharing it with free range sheep?

photo collage near the top of climb, roadway snaking up hillside below, green pastureland 

Photos nearing the top of the climb.

photo collage shows hairpin turns at top of climb

Epic set of seven hairpins leading to the dam: 2/10ths of a mile at 11.5%.

at top of climb, Stwlan Dam, misty day 

The imposing Stwlan Dam is the cherry on top of this epic bike climb.

aerial drone view shows roadway snaking up the green hillside to Stwlan Dam

Lyn Stwlan Reservoir was created by the Stwlan Dam. The first dam on this site was constructed in 1898 as part of a hydroelectric project in the area.  The reservoir fills and enlarges a glacially formed lake that obviously preexisted the dam.  The current dam is 800’ across and 110’ high.  Construction began on the current dam in 1957.

aerial drone view shows PJAMM Cyclist stands with bike next to roadway, hairpin turns below 

Below climb summary by PJAMM Cyclist’s Tayler Hockett:

I’d make a day of this! A truly amazing climb that twists up through ferns and roaming/grazing sheep to reach the dam. The view, smooth pavement, lush green ferns, and wandering sheep make this a must-do ride. Sitting at the top you hear the stillness and water, your friends can cheer you on as you watch them ride from the top. Bikes are not allowed on the dam but standing at the lookout point you can see the size and power of the hydroelectric bound surging water that you’d never know was there but for the physical struggle to the top. Bring food and water as there is not a lot going in the small, quiet town where the climb begins.

That’s a wrap!