Travelling to high elevations produces predictable physiological effects that respond to how quickly you ascend.
Acute mountain sickness
Headache, nausea and fatigue at altitude.
Which affects a substantial proportion of visitors above certain elevations.
Ascent rate
The main controllable factor.
Which guidelines specify in metres per day above a threshold.
Fitness
Not protective, and sometimes associated with ascending too fast.
Serious forms
Fluid on the lungs or brain requiring immediate descent.
Which is a medical emergency.
Why fitness does not protect you
Susceptibility to altitude illness has no reliable relationship with fitness, and fit travellers are sometimes at greater risk because they ascend faster.
Which is one of the more counterintuitive facts in travel health.
The controllable variable is ascent rate, and guidelines specify limits on how much elevation to gain per day above a threshold, with rest days built in.
Sleeping altitude
Where you sleep mattering more than the highest point reached.
Which is why climb high sleep low is standard advice.
Recognising serious illness
Confusion, breathlessness at rest and loss of coordination.
Which require immediate descent rather than observation.
Medication
Prophylaxis available and prescribed after assessment.
A general note
Anyone planning high-altitude travel should take specific medical advice.
What actually makes a trip go well
Very little of it is the things travel content concentrates on. It is not the property, the itinerary or the equipment. It is preparation on a small number of specific points, a pace that leaves room for things to go wrong, and enough humility to ask people who live there.
The trips that go badly are usually the ones where something checkable was not checked: an entry requirement, a health preparation, a transport connection, or the assumption that a place would be like somewhere else. All of those are answerable in advance and none takes long.
The preparation that repays itself
Entry requirements from the destination’s own authority. Travel health advice with enough lead time for vaccinations. A realistic daily budget including local transport, food and activities. Twenty words of the language. Somebody at home who knows roughly where you are.
That is an hour or two spread over the weeks before departure, and between them those five things prevent most of the situations that turn an ordinary problem into a serious one.
What travel writing tends to leave out
Most of it is written to inspire rather than to inform, which means it emphasises the extraordinary and skips the logistics. That is a reasonable commercial choice and it produces a systematic gap: the things that determine whether a trip works are rarely the things written about.
Entry requirements, health preparation, realistic budgeting and what a place is actually like on an ordinary Tuesday are all more consequential than any recommendation, and considerably less photogenic.
A general note
Entry requirements, health advice, safety conditions and local law differ enormously by destination and by nationality, and they change. Official sources for your own nationality and your specific destination are the only reliable reference.
On the destinations themselves
Almost every place is more ordinary and more interesting than its reputation. The reputation is built from a handful of images that a great many people have now seen, and arriving expecting them produces a disappointment that has nothing to do with the place.
The parts of a destination that people remember afterwards are generally not the ones they went for, which is an argument for leaving room in an itinerary rather than filling it. Whatever you plan, the unplanned hours are where most of it happens.
The travel that seems to be worth most
Longer stays in fewer places, some contact with people who live there rather than only with people paid to serve you, and a willingness to be uncomfortable occasionally. That is what the research on attitude change points at, and it is also what people describe when they talk about trips that mattered to them.
None of it requires money. Some of the most valuable travel is the cheapest, which is not something the industry has any interest in saying.
Where to get reliable information
Foreign ministries publish entry requirements and safety advice for their own nationals. Travel health services publish destination-specific medical guidance. National tourist boards publish practical information without a commercial interest in any particular property.
All three are free, current and specific to where you are actually going, which is more than can be said for most of what a search returns.
One habit worth adopting
Ask someone who lives there. Accommodation staff, drivers, shopkeepers and people at the next table know things no guide contains, and most of them are pleased to be asked.
It is also the part of travelling that people remember afterwards, which is a reasonable argument for it beyond the practical one.
A final caveat
Conditions, requirements and local circumstances change, and anything written at a point in time carries that date. Official sources for your nationality and destination are the reliable reference before any trip.