Roll up for the Machu mystery tour: Author Philippa Gregory is overawed by Peru’s incredible enigma – and under fire from piranhas

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Machu Picchu in Peru has been named as one of the new seven wonders of the world, and it does not disappoint. 

What is wondrous about it must be different for every hiker who makes the trek up the long Inca trail, or every tourist who comes more comfortably by train. 

But few people can resist the sense of awe at this amazing site.

Author Philippa Gregory explored Peru's magnificent Machu Picchu, an 80,000-acre site which sits nearly 8,000ft above sea level

Even today it still challenges with unanswered questions. 

Why was it abandoned only eight years after it was completed in about 1572? Why did the Spanish conquistadors never discover it as they hunted for the gold of the Inca? Why was it built in the first place? 

And how was it that people working without a written literature and cutting stone without iron tools could plan and construct such an extraordinary site, nearly 8,000ft above sea level, putting together terraces, palaces and temples without mortar? The enormous shaped boulders fit together like a 3D jigsaw puzzle of the gods.

I reached it the easy way – by the scenic train ride, the narrow track winding through gorges and across clean mountain rivers, to the town of Agua Caliente. 

I can assure you that there is nothing very wondrous about Agua Caliente – it exists as a starting point for the buses up the mountain and it is all market and no mystery, a lot of plastic and no archaeology.

The first thing that strikes the visitor about Machu Picchu is the scale – the whole site covers nearly 80,000 acres. The mystery city was probably built for an educated elite. Some of the religious buildings are aligned for sunrise and sunset, others are precisely placed to catch the rising moon.

Philippa and her friend, pictured, were suitably alarmed by their close encounters with piranhas during a fishing trip

I was shown around by a local guide who spoke of the American explorer who came upon the ruins while looking for somewhere else, of the extraordinary archaeological work that continues today, and the eccentric theories that only another civilisation could have created such a miracle of engineering. Ancient Egyptians? Aliens? Both?

However sceptical one might be, the ruins, their relationship to other sites in the ‘sacred valley’ nearby, and their inspiration from astronomy, makes you long to solve the mysteries yourself.

I came back down to earth at Cusco, capital of the Inca empire. It’s a hauntingly pretty town where a perfectly shaped Inca wall runs on one side of the street and exquisite medieval Spanish townhouses fill the other.

You can walk past the famous ‘angle stone’ on your way to the Coricancha palace, where the Inca temple forms the core and base of the later Spanish monastery built by the conquistadors to celebrate their victory.

When an earthquake hit Cusco in 1950, it destroyed the cathedral but the Inca temple remained standing – the guides say that the Inca stones were so perfectly fitted together that they could move apart and then rejoin without falling.

Inca culture is inspiring, but in Cusco the modern world is beautiful too. I stayed at Inkaterra La Casona, a 16th Century house now superbly restored with 11 suites, each with a super-sized bath and open fireplace.

The final part of my holiday was to the Peruvian Amazon. 

Philippa's vessel was this, a spacious riverboat from which motorboats took her out on daily excursions along the Amazon

To reach the Amazon by plane, you have to go through Lima. Actually, to fly to almost anywhere in Peru you have to go through Lima, and soon I’d had enough of the crowded, clogged, exuberant city. 

A Peruvian told me the wonderful myth of Lima: that conquistadors asked a defeated Incan where they should site their principal city and, in a great revenge joke, he suggested a rain-washed valley surrounded by sunny hills.

You can be in damp mist in Lima when it is clear just five minutes away.

From Lima I flew to Iquitos for a six-night Amazon riverboat adventure. Every day I went out on small motorboats with highly skilled guides and every day I came home to my generous-size cabin having seen something strange, rare or exotic.

I became accustomed to seeing a flamingo-coloured pink dolphin, breaking the surface of the river and showing a flash of shocking pink as it dived. Amazon kingfishers escorted the boats, and I saw a family of otters, a tiny spider monkey, hawks, parrots and orioles.

She also stopped by Cusco, capital of the Inca empire, pictured - a hauntingly pretty town where a perfectly shaped Inca wall runs on one side of the street and exquisite medieval Spanish townhouses fill the other

One day we were even offered the chance to swim in the Amazon, and catch piranha. I am sorry but I declined both. 

The water of the Amazon – chocolate-brown in colour and teeming with underwater life – is not inviting, and I don’t like fishing for any sort of fish, least of all fish with teeth. So I sat in the prow with a friend and planned to sit peaceably beside her as she dipped the bait in the water.

At one point a piranha snatched. As she jerked it out of the water, it swung towards me on her line, and slapped my hat. I saw the face, the eyes, the sharp little teeth. I screamed, my friend screamed, the boat rocked, she flung line and nearly rod back in the river and the piranha unhooked itself and vanished. 

Then, of course, as all serious fishermen do, we clung to each other and dissolved into giggles.

Philippa’s latest novel, Three Sisters, Three Queens, is out now in paperback, priced £8.99.