The headache usually arrives around midnight on the first night. You're in Cusco, or Kathmandu, or La Paz, and you're not sick exactly — just wrong-feeling, as if someone has turned the contrast down on everything.
Altitude sickness doesn't discriminate by fitness. Some of the strongest hikers we've encountered were laid flat in Cuzco while considerably less prepared travelers walked past unfazed. The variable is genetics, not willpower.
The single best thing you can do is what you almost certainly don't want to do: rest. Two acclimatisation days before ascending feels like wasted time until you're watching someone else's trip collapse on day three because they went straight up.
Drink water. Don't drink alcohol. Eat light. Sleep at a lower altitude than your highest point of the day. These aren't tips — they're the operating system for being at altitude without suffering.
adv.entu.re editorial