THE Lost City of the Incas, Machu Picchu, is lost no more. It's a Unesco World Heritage Site and has become so popular that the Peruvian government now limits the number of visitors, although not nearly as strictly as Unesco would like.
Between 1980 and 2000 visitor numbers trebled and have reached about one million a year. It's now considered an "at risk" site simply because of the pressure of visitors and the apparent unwillingness of the Peruvian government to do more to protect it. Helicopter flyovers are now banned, however, and there is a strictly-enforced daily visitor limit of 2500. Unesco wanted to see the limit set at about 900.
This means that unless you have stayed overnight in the small town of Aguas Calientes that has been crammed between mountain and river in the valley below the ruins, you're going to arrive at Machu Picchu in the company of several hundred other visitors.
It's one of the vexations of travel that some of the most heart-stopping sights on Earth often begin with the tedium of queues, security, barked orders and paperwork.
Worst of all is that among the hordes accompanying you are a surprising number of the inexplicably grumpy and rude.
It still astonishes me that so many people can look glum or bored when they are about to become some of the privileged minority to see for themselves places the majority of people can only dream about visiting.
As I wove around milling tour groups, paddled through the overworked loos, and battled with pages of tickets and permits I did briefly wonder why I'd bothered - or at least not tried harder to get to Machu Picchu about 20 years earlier. And this was the rainy season, when visitor numbers are relatively low.
However, once through the entrance gate and on to the mountain ridge where the Incas built their city-sanctuary, the crowds dispersed. That's another of the astonishments of such places - it is still remarkably easy to escape the masses and find a spot to mentally dust off the petty annoyances of travel and absorb one's surroundings.
If you take a guide with you, they will usually lead you first to an Inca stone platform where there is a classic, but still breathtaking view of the ruins. (At 2430m, if you haven't acclimatised well Machu Picchu can literally leave you gasping for breath - especially as there are hundreds of steps).
Although the Andean skies were full of clouds and mist still snaked around Waynnapichu, the steep hummock of a mountain that stands sentinel to the north of the ruins, from this vantage point I could still see clearly across what is one of the greatest ruined cities in the world.
Machu Picchu was built by the Incas, who until the mid 16th century ruled the largest pre-Columbian empire in South America.
As their capital was in Cusco, even higher in the Andes, no one is exactly sure why they also built spectacular Machu Picchu, especially as it was so inaccessible, being many days of arduous mountain walking from Cusco.
The exact purpose of Machu Picchu might still be debated more than 500 years after the Incas deserted their sanctuary, but much is now known about the functions of the dozens of intact buildings and "neighbourhoods" in this city in the clouds.
Closest to the first lookout point are the agricultural terraces where the Incas grew potatoes, corn and even cotton. The Incas would have kept llamas too and their dung would have been used to fertilise the terraces. A sophisticated water supply system had also been created to water these crops, as well as to provide water for the inhabitants.
The terraces were so well built that they are still in use in many parts of Peru and the canals also remain functional.
Machu Picchu's setting is so stunning that it can be hard to drag one's eyes away from the views to concentrate on the intricacies of the buildings themselves. But not to do so is to miss what experts regard as one of the greatest examples of man's use of natural stone in the world.
Two of the great 15th century Inca kings, Pachacuti and Tupac, were in charge of the building of Machu Picchu and it was a formidable feat.
Although the granite used for much of its construction was available on the mountain itself, the transport of it around the site with its near-vertical hillsides and then hoisting it into position would have been exceptionally challenging. All the stone was cut with metal tools, utilising natural fracture lines in the granite.
The Incas, although they knew about the wheel (it was used in children's toys, for example) did not use this innovation in daily life. Instead it is thought the stones were moved into position by rolling them along wooden beams placed on earthen ramps.
If there is any "secret" to the city, it is probably the way the workforce was organised, as it was a hugely labour-intensive process.
One of the first things you notice while wandering around the site is that the Incas used many different forms of construction.
The most important buildings, such as the Temple of the Sun and the Royal Palace, are made of granite blocks so carefully cut and finished that they fit perfectly together without any mortar. Some of the blocks apparently have up to 30 facets to ensure they fit so closely that even today it's impossible to insert a needle between the blocks.
The Andes is earthquake-prone, something the Incas were well aware of. They used techniques including trapezoid doors and windows for extra strength, walls inclined inwards slightly and L-shaped blocks to tie corners together. All these features, including preferring to avoid mortar for their most special buildings, helped earthquake-proof them.
For the terraces and the homes of commoners, the Incas used a combination of adobe walls and field stones that were mortared in place. All the buildings would originally have had thatched roofs.
Sometimes the Incas combined both drystone and mortaring techniques and sometimes they even incorporated a third element, natural rock outcrops on the site.
One of the most spectacular examples of this is the Temple of the Condor (the Andean Condor is a species of vulture). The natural shape of a massive boulder was further worked by master stonemasons to create the outline of a condor's outspread wings. They then fashioned stone at the base of the wings to create the bird's head and neck feathers.
One of the most remarkable locations among the ruins is the Sacred Plaza, around which are the most important buildings in the city, including the Main Temple, the Temple of the Three Windows (which has wonderful acoustics) and the Intiwatana, the Hitching Place of the Sun.
The Incas, who worshipped the sun as their supreme god, believed that at the two equinoxes (when the sun is directly above the stone creating no shadow at all) the sun could be hitched to this upright stone.
Effectively it was functioning as a giant astronomic clock or calendar, which was of vital importance to the Incas not only because of their beliefs but because of their more practical reliance on agriculture.
The Intiwatana is the only such structure left standing in the former Incan empire as the Spanish destroyed all the others. The Incas believed that if this stone was damaged or removed, the spirituality of the site was lost, so the fact this one is intact has led to some visitors believing that the power of the Incas' sun god is still tethered to the stone.
This is a perfect place to pause and absorb the atmosphere, whether or not you believe, as some do, that this stone emanates deep spiritual energy and is on a magnetic hotspot.
What I do know is that the view from the plaza is magic from a geographical perspective.
The monumental buildings are awe-inspiring but sometimes it's the small details that are almost easier to relate to.
Cascading down through the site are the Ritual Fountains, 16 stone baths and linking waterfalls that were probably used for ritual bathing. The stonework is intricate, still immaculate and the water is still flowing today.
The higher one climbs in the site, the fewer the visitors, so for this reason alone it's worth slogging up in the Incas' footsteps to the terraces where the most classic of Machu Picchu photographs are taken.
Only as I made my way back to the entrance and the shuttle bus stop did the clouds boil up the valley again and rain bucket down.
If the sun god was still around Machu Picchu, I'd caught him in a generous mood.