Inca trail to machu picchu

How hard is it?
That will depend on you and what you're used to. It's generally reckoned to be a strenuous hike but there's no rock-climbing or glacier-walking involved, so no technical expertise is required. The difficulty comes largely from the repeated steep ascents and descents, and from the high altitude. The climb to the first pass takes you up from around 9,800 feet to more than 13000 feet in a relatively short space, followed by a descent of around 3000 feet. After the second pass at 12,631 feet, things generally become easier. You should remember also that unless you go with an organized tour or hire porters you will need to carry camping and cooking equipment, clothing and food for three or four days, all of which makes for a fairly heavy pack.
How fit do I need to be?
The fitter you are, the more you will enjoy it. Conversely, the less fit you are, the less you'll enjoy it. If you're extremely unfit, you may even fail to enjoy it to the point of collapsing in a lifeless heap somewhere along the way and having to be buried on the spot by your fitter companions. In the absence of any agreed universal measure of fitness, consider that for a relative fit fifty-one year old (me) it was difficult but manageable. I found the second day and the first part of the third very tough indeed, but thereafter things became easier. However, don't be deceived. It is very hard work in places and you are likely to be carrying a heavier pack than you are normally used to. A better than average standard of fitness is probably highly desirable, if not absolutely required. If you want to prepare yourself, hiking is the most obviously appropriate activity but anything that builds stamina such as running or swimming is also useful. Stamina is more important than strength or speed; being able to bench-press five hundred pounds will probably not help unless you intend to walk the Trail on your hands.
What about altitude?
The Inca Trail is high enough that some people do have problems with the altitude, LuAnn and me included. Being short of breath is relatively common and is not, by itself, cause for concern. On the other hand, severe dizziness, loss of coordination and concentration, severely irregular (Cheyne-Stokes) breathing, and death from pulmonary or cerebral edema are generally regarded as more serious symptoms of mountain sickness. The chances are that you won't experience any ill-effects from the altitude, but it is definitely worth spending some time acclimatizing before you set out, with Cusco being the obvious place to do this. If you go straight from sea-level to the Inca Trail you are much more likely to have problems, as we did. It's been suggested that 3-4 days acclimatization, including day-hikes in the Cusco region, should be considered a minimum. Again, getting fit beforehand will also make life easier.
What's the best time of year to go?
The 'dry' season from April to October seems to be generally considered preferable, at least as far as weather is concerned. The driest months are from May to September, winter months in the Southern hemisphere. Temperatures can fall to below freezing above 10,000 feet, and it may be windy from August onwards. During the spring, September to December, there are likely to be early afternoon showers (sometimes accompanied by thunderstorms) of short duration, and it may be cloudy and overcast. Nights during this season are clear (which means cold at high altitude). The rainy season is from December to May. There is likely to be heavy rain for two to three hours every afternoon, as well as the possibility of light showers that continue over a longer period. Walking conditions are difficult and streams may become impassable. Note that just as anywhere else in the world, these are general tendencies. You could have a dry day in December and you could get rained on in July. Note also that there's a wide variation in temperature, dependent on altitude and time of day. Some guidebooks report that it can vary by up to 40 degrees, so it can be quite warm during the day at low altitudes and below freezing higher up during the night.
Is it dangerous?
Not especially. It's a three or four day walk in a fairly remote area. There are places where you could fall and hurt yourself, or even kill yourself if you really work at it, but unless you're very careless or clumsy it's not very likely. On the other hand, it's not a good place to have a medical emergency. If you have a tendency towards cardiac arrest, passing suddenly into a diabetic coma, epileptic fits or whatever, try to arrange for it to happen somewhere else.
I'm scared of heights - will I be able to walk the Trail?
If the words 'Inca Trail' call up images of swaying rope bridges over deep ravines and narrow paths carved into the faces of sheer precipices, relax. There's nothing like that. And it's a walking trail, so you don't need to do any mountaineering. There are a few steep descents, and there are some places where there is a drop-off on one side of the roadway. However, even people who don't like heights should be able to walk these stretches quite comfortably.
What about wild animals?
One section of the Trail is optimistically marked "Zona de Osos" ("Bear Zone"), but your chances of stumbling across a bear are probably very slight. Predatory wildlife on the Inca Trail consists mainly of the local pigs and dogs around Wayllabamba (who will eat anything that you leave outside, including boots, rucksacks and plastic garbage bags) and biting flies, which will eat you up. The insects, particularly around the Pacamayo, are extremely fierce. There have also been reports of chiggers and other pests near Wayllabamba. A good insect repellent is a necessity.
Is the Trail crowded?
You're likely to meet about 200 other people per day on the Trail, including large groups with guides and porters. The crowding is evidently particularly bad during the popular summer months. This has an inevitable impact, both on the facilities and the environment. Whatever the conditions on the Trail, Machu Picchu is usually Tourist Central.
Toilet facilities?
They're scarce. There are pit toilets at the campsites, but the rest of the time you're on your own. What this means above all else is that you need to be a good citizen of the wilderness and obey the rules. Since it's impractical to backpack your crap out of the region along with the rest of your rubbish, this means that when you have to go, you should go a long way away from the Trail, and bury your excrement properly after you're done. This is not an especially pleasant task, but it must be done. And when you're at the campsites, use the facilities available.