The place today called Macchu Picchu is a small Inca town which stands on the ridge below the mountain peak called Huania Picchu, in a position of extraordinary beauty, overlooking the Urubamba valley, some 80 Kms north-west of Cusco. The town is not visible from the valley below and, although it may seem incredible, there is no proof that it was ever visited by the Spaniards: it was forgotten, probably because it had been abandoned for a number of years ‒ perhaps due to viral epidemics ‒ already before the Conquest. Local farmers of course continued to live in the area, but the city was overgrown by the jungle and brought to the attention of the archeologists only at the beginning of the 20th century by the american explorer Hiram Bingham. We do not know precisely why Macchu Picchu was constructed; certainly it was not a stronghold, because water is supplied by an aqueduct which starts, in plain view, from a source located outside the walls of the town. The elaborate architecture, and in particular the presence of perfect stone walls and of double jamb doorways, shows that it was frequented by the king and by the Inca elite. It was, very probably, also a sacred, pilgrimage centre. The town is in fact perfectly and wonderfully integrated in the nature around, so much so that the masonry structures mix with the natural rocks in bewildering harmony. A wonderful example of how the Incas conceived and plasmated nature at Macchu Picchu is the so-called Temple of the Condor. Here natural boulders of rocks seem to form two open bird’s wings; on the ground, a sculpted stone helps the eye to imagine the bird's head, with a characteristic ruff of white feathers surrounding the base of the neck. The result is the image of a huge condor, ready to take off ‒ or just landed to visit the town. Another example is the so-called sacred rock, a large stone boulder that an artist sculpted as a replica of the profile of the mountains visible on the background. As we have seen, the relationship of the Incas with the sky was complex and elaborate, and Macchu Picchu is no exception. The entire town was a sacred place and as a consequence it was connected in many ways with the entire landscape, including the sky. First of all, interest for the winter solstice is clealry visible in the street plan and in one of the most perfect buildings, the so-called Torreon. The building is similar to a large tower, and its main window points at sunrise on the June – winter – solstice. The summer solstice was also observed from another structure, the so-called Intimachay cave. It is a natural cave which was modified in such a way as to allow astronomical observations ‒ perhaps also of the Moon ‒ from the tunnel inside. The most sacred area of Macchu Picchu, the so-called Sacred Plaza, opens to June solstice sunrise to the northeast. The midsummer ‒ December ‒ Sun sets instead in the direction of a recently rediscovered site, Llactapata, which was a sort of companion of Machhu Picchu, located on the opposite ridge of the Urubamba valley. Finally, on the summit of the terrace over the sacred plaza we find an enigmatic megalith, traditionally called the Intihuatana or Sun Stone. Despite the name, the purpose of this monolith carved in granite is not clear at all; maybe it was only a symbol, as it is too massive to be used to measure shadows as a gnomon. What is certain is that the profile of the stone resembles the peak of the mountain behind, confirming once again to us the complexity of the relationship of Inca architecture with the natural environment.