Altitude does not announce itself. At 1,200 meters the air is simply thinner, and the first sessions feel as if the rope, the plan, the pace have been quietly recalibrated overnight.
Then the light: sharper at elevation, cooler in color, throwing edges sea-level haze never allows. Every familiar movement must be renegotiated. Paces held easily at sea level need reconsideration, and rest arrives sooner and insists on being taken seriously.
None of this is a problem; it is information. What comes back down is not fatigue but a recalibrated sense of effort — a cleaner answer to what a given pace actually costs.