Alto del Castillo

Overview

Alto del Castillo is a hors catégorie (HC) climb in Colombia, and it earns that rating on length alone. Over 39.2 km it climbs from a start elevation of 1,049 m to a summit at 3,782 m, for a net elevation gain of 2,733 m at an average gradient of 6.96%. This is a full-day mountain, not a punchy afternoon effort — a sustained haul into thin air that finishes well above where most riders spend their time.

The number that reshapes the whole effort is total ascent: 4,181 m against a net gain of 2,733 m. That 1,448 m gap is climbing you do that the summit elevation never credits you for — descents and dips mid-climb that you have to re-climb. Every metre lost has to be won back, so the physiological cost is closer to a 4,181 m day than the 2,733 m the profile summary suggests. Plan and fuel for the larger number.

How the Gradient Unfolds

The 6.96% average is an accounting artifact, not a description of the road. With 1,448 m of hidden re-climbing, the gradient swings hard around that mean — flatter and downhill stretches drag the average down, which means the climbing sections have to sit well above 6.96% to compensate.

• Recovery zones: flatter and descending sections where the road gives back elevation, then demands it again.
• Repeated short climbs: expect several distinct ramps rather than one continuous wall, separated by the dips.
• The steepest ramp: the pitches doing the compensating are noticeably harder than the average — treat any sustained double-digit section as the crux, not a surprise.

Pacing Notes

On an undulating climb like this, even-speed pacing is a trap: holding a fixed pace means spiking your power on every ramp and coasting through the dips, which torches your legs early. Ride even-effort instead. Anchor your intensity to a target power below your sustainable power output and let speed rise and fall with the terrain — fast through the flats and descents, patient on the ramps.

If you do not know that ceiling, set it before you leave home with the FTP estimator. At 39.2 km and nearly 3,800 m of altitude, going out too hard is unrecoverable.

Gearing

The average tells you nothing about gearing here; the steepest ramps do. On a climb built from repeated pitches steeper than 6.96% at altitude, gear for the worst section, not the mean. Run a compact (50/34) or sub-compact chainset paired with a wide-range cassette — a 34×32 or 34×34 low gear so you can keep cadence up on the crux ramps without grinding. Check your setup before the ride: confirm the cassette actually fits your derailleur and that the low gear is there. You do not want to discover a missing sprocket 30 km in.

Summary

• Length: 39.2 km
• Average gradient: 6.96%
• Net elevation gain: 2,733 m
• Total ascent: 4,181 m
• Category: HC

Alto del Castillo is a length-and-altitude climb where the undulation is the real story — 4,181 m of ascent for 2,733 m of net gain. Pace by effort, gear for the steep ramps, and respect the extra 1,448 m the summit height never shows.