BETA — measurements and names under active refinement. Seen a sign, a gate, or a better name? Submit an update no account needed · photos welcome via GitHub

Devil's Staircase

841.5 m · net rise 111.1 m · total ascent 114.8 m · overall 13.2% · confidence: high · Coed Nant-yr-hwch · Powys

Shape: sustained — 36% of the climbing sits in a quarter of the distance; longest continuous stretch at 10%+ is 243 m.

Matches: Another 100 Greatest Cycling Climbs (Simon Warren), 100 Greatest Cycling Climbs (Simon Warren) — No. 93 in the app's 2026 numbering (earlier recorded as Another 100 — the editions appear to have reshuffled; both facts retained).

≈ Overhead cover (tree canopy or structures) spans 8% of this route — detected by comparing the surface model (DSM, treetops and rooftops) against the terrain model (DTM, bare ground). Under cover the bare-ground model is built from fewer laser returns, so metre-scale readings can wobble; maxima whose window sits in a covered zone are marked ≈ below — less certain — the flag does not say whether the true value is higher or lower. Longer windows average over more clean ground and are steadier.

Gradient ladder what do windows mean?

Window	Maximum	Located at
2 m (diagnostic)	37%	322–324 m
3 m (diagnostic)	36%	321–324 m
5 m	29%	443–448 m
10 m	27%	308–318 m
20 m	24.7%	308–328 m
25 m	24.5%	375–400 m
50 m	23.0%	347–397 m
100 m	22.5%	307–407 m

may_start_earliermay_continue_beyond_end Extent detection suggests reviewing where this climb starts/ends.

Map

Check this route yourself: Google Maps route via their router · Street View at the base where coverage exists · geojson.io our exact measured line · OpenTopoMap

This climb's data: OCL JSON — the full gradient ladder, quality flags and provenance in the OpenClimb Ladder format.

Ridden it, or know better? Submit data for this climb no account needed

Devil's Staircase LiDAR hillshade map with contours

Profile

Reported values vs. measurement

Source	Claim	Evidence	Best-matching window
Road sign / OSM incline tag	25%	road_sign	20 m (+0.3 pp)

Provenance

{
  "analysis_version": "0.1.0",
  "sample_interval_m": 1.0,
  "interpolation": "bilinear",
  "smoothing": "none",
  "gradient_windows_m": [
    5.0,
    10.0,
    20.0,
    25.0,
    50.0,
    100.0
  ],
  "diagnostic_windows_m": [
    2.0,
    3.0
  ],
  "elevation_crs": "EPSG:27700",
  "elevation_resolution_m": 1.0,
  "elevation_tiles": [
    "data/cache/wales/dtm_1m/wg_del_22_282255_20220114dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_22_282256_20220114dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_26_283255_20220226dtm.tif",
    "data/cache/wales/dtm_1m/wg_del_26_283256_20220226dtm.tif"
  ],
  "calculated_at": "2026-08-12T09:11:49+00:00",
  "road_source": "OpenStreetMap (local PBF extract)",
  "road_attribution": "\u00a9 OpenStreetMap contributors, ODbL",
  "osm_pbf_path": "data/cache/pbf/wales-2026-08-11.osm.pbf",
  "osm_snapshot": "2026-08-10T20:21:40Z",
  "elevation_provider": "Welsh Government",
  "elevation_dataset": "Welsh Government LiDAR 1m DTM (2020-2023)",
  "elevation_licence": "Open Government Licence v3 \u2014 \u00a9 Crown copyright Welsh Government",
  "elevation_catalogue_layer": "geonode:welsh_government_lidar_tile_catalogue_2020_2023",
  "elevation_tile_ids": [
    "wg_del_22_282255_20220114dtm.tif",
    "wg_del_22_282256_20220114dtm.tif",
    "wg_del_26_283255_20220226dtm.tif",
    "wg_del_26_283256_20220226dtm.tif"
  ],
  "elevation_capture_dates": [
    "14-01-2022",
    "26-02-2022"
  ],
  "climb_origin": "named",
  "notes": "Abergwesyn pass, hairpinned section. Famous audax/sportive climb. EXTENDED by graph walk: +1 segment(s) at base, +0 at top (stop: base=no_descending_continuation, top=no_ascending_continuation; min_avg=2.0%). Review before adopting."
}