To go to Peru and not visit Machu Picchu is kind of like going to Paris and ignoring the Eiffel Tower: It simply can’t be done. And most people don’t ignore this important Pre-Columbian site since it’s the most visited attraction in this South American country.

What makes Machu Picchu so darned special? For one thing, it’s the most preserved remains of the once-mighty Inca Empire. Sitting at the 2,430-meter (7,970-foot) level of Machu Picchu (Old Peak) Mountain, the site is stunningly, hauntingly beautiful.

Built around 1450 for the Emperor Pachacuti, the palace was abandoned a century later. Miraculously, the site escaped the plundering and destruction of the Spanish conquistadores who destroyed everything Inca they could get their hands on.

Over the centuries, the site became overgrown with vegetation. Few outside the local area even knew of its existence. The lost city of the Incas remained untouched until 1911. That’s when Hiram Bingham, an American historian and explorer, visited, en route home from a conference in Chile, the region looking for Inca ruins.

Bingham hit the Mother Lode of not only Inca ruins but of worldwide archeological ruins with Machu Picchu. The palatial estate is one of the most important archeological ruins in the world.

This fortress in the clouds is one of the best examples of Incan architecture, built at a time when the Incas were at their height. Structures are built of stone, which is not unusual for this time frame anywhere in the world. What makes Machu Picchu an engineering marvel, however, is these stones and rocks were fitted together without the use of mortar. The rocks fit together so tightly, a knife blade cannot be inserted between them. The stone construction blends in perfectly with the surrounding mountains.

Machu Picchu is laid out in sections. There’s an urban section and an agricultural section, an upper old town where the temples are located and a lower new town where warehouses can be found. Altogether, about 200 buildings can be found at Machu Picchu.

One of the most spectacular remains is the Temple of the Sun that majestically overlooks the Urubamba River, which surrounds the site on three sides, and the Sacred Valley below. This is another engineering marvel, one that has astrological overtones. At the summer solstice, the sun shines through a temple window, in perfect alignment with the boulder the temple is constructed around and a mountain peak. Another remarkable elements is a ceremonial stone known as the Intihuatana stone, which was situated within a precise location that perfectly aligns with the two annual equinoxes.

Machu Picchu is, however, more than a palatial estate for Incan rulers. Because of its strategic location, it may have been a military stronghold. It also may have religious connotations because of the temples where human sacrifices to appease the gods were made. Not all the sacrificed people were given proper burials, and their remains have been found at the site.

Another awesome sight is the 700 stone terraces built on the slopes. These terraces served multiple purposes: plots to grow farm crops; conserve water and to fight erosion.

Historians today continue to study Machu Picchu, hoping to unearth more of its mysteries. The biggest question remains why the Incas built Machu Picchu. This may remain one of the biggest unsolved mysteries because the Incas had no written language.

There are a couple of ways to get to Machu Picchu. Most people take the train from Cusco, 50-miles away, riding a bus for the final miles. If you’re hardier traveler in tip-top physical condition, you might consider taking a multi-day trek on the Inca Trail. This is the traditional route that generations of Incas, and later Bingham, took to reach the site.