If you can only do one, choose Humantay Lake if you are newer to altitude, short of time or travelling with less experienced walkers. Choose Rainbow Mountain if you are well acclimatised, fit and want the bigger, higher day. Do neither on your first two days in Cusco.
The criteria
Time: both are done as long day trips from Cusco with a very early start, typically leaving in the small hours of the morning and returning in the afternoon or evening. Much of the day is spent in a vehicle. Humantay is generally the shorter outing.
Altitude: this is the main difference. Humantay Lake sits at about 4,200 m, with a trailhead lower than that. The Rainbow Mountain viewpoint is around 5,000 m, a significant step higher, which means a higher chance of symptoms for those who are not acclimatised.
Effort: the Humantay walk is a steady, relatively short climb that is hard mainly because of the thin air. The Rainbow Mountain trail is longer and finishes with a steep section at very high altitude.
Cost level: both are modest day-tour prices by international standards, with the spread between operators mainly reflecting group size, food and transport. Entry fees to local communities are often charged separately.
Crowds: both are popular and can be busy in the dry season, and the crowd tends to peak at the viewpoint in the middle of the morning.
Season: the dry months from roughly May to September have the clearest views, but also the coldest mornings. In the rainy season, cloud, mud and snow can reduce visibility and, at times, access.
Risk: altitude sickness, cold and fatigue are the main risks. Weather at these heights changes quickly.
What you actually get
Humantay delivers a turquoise glacial lake beneath a snow-capped peak, with a view that photographs well on a clear morning. The pay-off comes relatively early in the day, and the setting feels like a true mountain landscape even though you are within a day trip of Cusco. See Humantay Lake for the walk in detail.
Rainbow Mountain offers striped hillsides in rust, ochre and green, with a high-altitude panorama and a view toward other glaciated peaks. The colours depend heavily on light and weather, and they often look more muted in person than in promotional pictures, which is why some visitors find the effort higher than the reward. See whether Rainbow Mountain is worth it for more on that, and the Rainbow Mountain for the route itself.
The day itself, hour by hour
Both days follow the same rhythm. A pickup in the dark, a long drive on mountain roads with a stop for breakfast, a walk of a few hours, a picnic or packed lunch, and a return that can reach the early evening. Expect to be tired, cold at the start and hot in the sun by midday.
On the Humantay day, the walk begins from a trailhead reached after a bumpy ride, and the climb to the lake is steady, with frequent pauses. You spend a limited time at the shore, since the groups are scheduled.
On the Rainbow Mountain day the vehicle ride is typically longer, and the final ascent is the hardest section. Time at the top is short, and the descent can be slippery in wet weather. In both cases, ask the operator what the schedule is, whether breakfast and lunch are included and what the group size is, because these details differ more than the destinations do.
Preparing your body and kit
The best preparation is time at altitude beforehand, not training. Spend a few days in Cusco and the Sacred Valley first, sleep lower if you can, and keep alcohol light the evening before. For what helps and what does not, see acclimatisation, and for the symptoms, altitude sickness.
Pack layers: a warm hat, gloves, a windproof shell and sun protection are essential at these heights, since conditions can shift from freezing wind to strong sun within an hour. Good shoes with grip matter more than anything fancy, and a day pack with water and snacks is enough. Some visitors consider hiring a horse for part of the Rainbow Mountain route; discuss the terms and the welfare of the animals with the operator beforehand, and be aware that this does not remove the altitude risk.
Choosing an operator
Because both hikes are sold as day trips from Cusco, there is a wide spread of operators and prices, and the cheapest option is not always the best. Group size, guide experience, the quality of the vehicle, whether oxygen and a first-aid kit are carried and what the plan is if someone becomes unwell are the points that matter.
Read choosing a trekking agency before booking, and compare what is included, such as meals, entry fees and transport. If you are buying in the city the day before, ask when the trip leaves and where you will be collected. See Cusco tours to understand how day-tour booking usually works.
Verdict by traveller type
Beginners at altitude, families with older children and those with a short trip: Humantay Lake.
Fit, well-acclimatised hikers who want a bigger day: Rainbow Mountain, ideally after a few days in the region.
Photographers: Humantay is the more dependable scene, particularly on a clear morning. Rainbow Mountain rewards good light and patience.
Anyone planning the Salkantay trek: Humantay is often included on that route, so you may not need a separate trip.
The answer changes if the weather is poor, if you feel unwell on the morning, or if you have a heart or lung condition, in which case neither may be the right choice.
Frequently asked questions
Can I do both in one trip?
Yes, but not back to back. Leave a rest day between them and do them after you have spent a few days at altitude.
Are they suitable for children?
Humantay is more realistic for older children who are used to walking. Rainbow Mountain is a harder choice because of its height. Discuss any child's health with a doctor first.
Which is better in the rainy season?
Neither is at its best. Cloud can hide the views and the paths turn muddy. Humantay is generally the safer bet because it is lower and shorter, but ask your operator about current conditions.
What time should I expect to leave Cusco?
Very early, usually well before dawn. Confirm the pickup time and place when you book, and go to bed early the night before.
Do I need to book in advance?
In the dry season it is wise to book a day or two ahead, particularly in school holidays. There is no permit system like the Inca Trail's, so late bookings are often possible.
Is a horse a good idea?
It can help on part of the Rainbow Mountain route for people who are tired, but it does not reduce altitude risk, and it adds a cost. Ask the operator how the animals are treated.
Which one has the better view?
That depends on weather and what you like. Humantay offers a lake and a glacier; Rainbow Mountain offers colour and a wide high-altitude panorama. Both depend on clear skies.