If our trip to South America was a book, some sort of road trip adventure with a narrative arc, then the Inca Trail would probably be the climactic chapter. That's the way we had both built it up in our heads, the defining moment which the whole trip had been leading up to.

Partly this was because the Inca Trail and Machu Picchu are generally ranked amongst those once-in-a-lifetime, 'bucket list' experiences. But it was also because we weren't sure we'd be able to finish the trek. The classic Inca Trail is a 4-day, 26-mile slog over mountainous, high altitude terrain, and neither of us had ever done anything like it. In the lead-up to our trip we'd worked ourselves into a frenzy of self-doubt after reading countless blogs and forum posts by people who'd struggled or, in some cases, failed to complete the trek.

Day 1: Piscacucho to Ayapata

After months of fretting over whether we'd bought the right kit, whether we'd done enough training and whether our bodies would cope with the altitude, the day finally arrived, and we were picked up from our hotel in Cusco at a bleary-eyed 4.30 AM. As the sun began to creep up over the horizon we headed north west through the Sacred Valley to the starting point of the Inca Trail, at a place called Piscacucho.

We chose to hike the trail with a company called Alpaca Expeditions on account of their excellent TripAdvisor reviews, and we were very happy with our choice. Alpaca have a superhuman team of porters who run ahead of you on the trail each day, carrying a whole campsite on their backs: tents, sleeping bags, portable toilets, kitchen equipment and more. Our guides were José, a serious-looking guy with a dry sense of humour, and Filio, an indefatigably cheerful chap with a penchant for chicha, an alcoholic drink made from fermented corn that is consumed across the Andean region.

The trail started gently enough, following the course of the fast-flowing Urubamba river. We passed through small villages and hamlets where enterprising locals were selling drinks or renting out their toilet for a few soles, and where the porters stopped for a fortifying glass of chicha, or 'Inca Red Bull' as José called it.

Access to the Inca Trail is far more regulated than it used to be, in an effort to protect the trail from the negative effects of over-tourism. Only 500 people are allowed to begin the trail each day, and around 300 permits a day are reserved for guides and porters. One of the nice things about the hike was the number of times that Polly and I basically found ourselves hiking alone, with our group spreading out as everyone found their own pace.

The Inca Trail is about more than just getting to Machu Picchu; we visited a host of other Inca sites along the way, and without the crowds that you find elsewhere in the Sacred Valley. Places like the abandoned settlement of Patallacta and the hill fort at Willkaraqay, both of which we passed on our first few hours of the hike, can only be accessed via the Inca Trail.

As midday approached we began to climb steeper slopes, the warm sun beating down on us, and by the time we reached our first lunch stop we felt pretty out of breath. We quenched our thirst with a cup of cold chicha morada, a delicious non-alcoholic juice made from purple corn, and chatted wth our fellow hikers about the trek so far. We felt a little bit anxious; day one was supposed to be easy, but we'd both found the morning fairly challenging.

There was no let-up after lunch, with a sustained and steep uphill climb, and we both decided to deploy the walking poles that we'd rented from Alpaca for the first time. Once we'd settled into a rhythm the poles made a huge difference; if you get your technique right, it's almost like you have another pair of legs to support you and propel you up the hill.

When we arrived at our first campsite, we couldn't quite believe it; we were there about an hour ahead of schedule, and after we started using the poles the uphill climb really hadn't seemed so bad. For the first time we started to feel confident that we would make it to the end of the Inca Trail after all. We celebrated with a cold beer purchased from an entrepreneurial local lady, who appeared at our campsite at just the right moment.

Day 2: Ayapata to Chaquicocha

The second day of the Inca Trail was the day that we'd been dreading for months, billed as the longest, steepest and most arduous part of the trek. We were woken up at 4 AM to begin our ascent to Dead Woman's Pass, the highest point of the trail at 4,215 metres above sea level.

Our poles were out once again as we slowly scaled the mountain under a dull grey sky. Once we crossed the 4,000 metre threshold the air became so thin that we could only manage a few steps at a time, stopping every couple of minutes to lean against a rock and get our breath back. The views at this point were simply stunning; a thick bank of cloud was moving swiftly up the valley, clinging to the craggy mountains and obscuring the valley floor down below. A few hardy llamas grazed where the ground was flat enough, and we were surprised to see a few hummmingbirds flitting about at this altitude.

The final few dozen steps were one of the hardest sections of the trek, with the pass seeming to hover just out of reach as we struggled onwards. Finally we reached the sign marking the highest part of the trail, and we dumped our bags on the floor. We had hoped to celebrate our achievement by stopping for a rest and cracking open the pack of Oreos that we'd been saving, but the mountains had other ideas.

Up until now we'd enjoyed surprisingly good weather, given that November is the beginning of the rainy season, but suddenly the weather turned. With barely any warning, the clouds that had been gathering overhead started pelting us with a shower of icy rain.

We scrambled down the other side of the mountain, stopping briefly to struggle and swear our way into our waterproof trousers, fingers already numb from the freezing rain. By the time we'd successfully donned our waterproofs we were already soaked through and feeling miserable, dealt a harsh lesson in how quickly things can change in the high Andes.

The descent was perhaps even worse than the ascent; the uneven Inca steps were slick with rain, and we had to carefully pick our way down the slope using the walking poles for support. Luckily the rain gradually eased off, and the sun began to dry us out as we approached our lunch spot.

The second pass of the day was almost as high, 4,000 metres above sea level, but the ascent was easier and the weather was kind to us. On the way up we stopped at an Inca watch tower, with stunning views of Dead Woman's Pass. Looking back at the trail we had descended earlier in the day, we couldn't quite believe that we'd made it this far; in places the path looked almost vertical.

We stopped for a snack at the top of the second pass, before making what was probably the most difficult descent of the whole trek. The Inca Trail is an incredible feat of engineering, with paths and staircases negotiating improbably steep mountain terrain, but certain sections haven't aged so well. We struggled down huge steps, some knee high, some even higher; in other places, the steps just disappeared and we had to clamber down over bare rocks.

But it was worth it for the views; on this side of the mountains the landscape changed completely, from the sparse vegetation of the high-altitude paramo to a warm, tropical environment carpeted in lush jungle. This part of the Andes is full of little micro-climates, with two sides of the same mountain supporting radically different flora and fauna. The scenery reached a dramatic crescendo at Sayacmarca, a sprawling Inca site on the side of the mountain. The whole of the valley below was draped with clouds, so that the fortress appeared to be almost floating in the sky.

We arrived at our second campsite exhausted but triumphant. Although there had been some hairy moments, we'd made it to the end of the dreaded day two in one piece. Whatever tomorrow had to throw at us, we now felt sure that we'd broken the back of the Inca Trail, and that we'd make it to the end.

Day 3: Chaquicocha to Wiñay Wayna

We enjoyed a more relaxed start to our third day, rising at a leisurely 5 AM. We were incredibly lucky with the weather on our Inca Trail hike, and it was another warm and sunny day as we made our way up a gradual incline to the spectacular ruins at Phuyupatamarca, known as the 'city above the clouds'.

From here it was all downhill, a relentless plod down a knee-jarring staircase known as the 'Gringo Killer'. As we descended, the cloud forest closed in around us, the sides of the mountain wet with moss and lichens. A couple of times the trail passed through a tunnel in the rock; in other places, little streams and waterfalls made the path dangerously slippery. Far below us we caught sight of the Urubamba river surging through the valley, and everywhere there were butterflies dancing around our heads.

Around midday we reached Intipata, a set of spectacular Inca terraces overlooking the valley below. Here we stopped to sit and take in the magnificent landscape laid out before us, and to reflect on the fact that we had completed 90% of the Inca Trail. Just a short distance away was our final campsite, where we had the whole afternoon to relax and prepare for Machu Picchu the next day.

After lunch we decided to brave the bollock-shrivellingly cold showers at the campsite, which did at least make us feel clean for the first time in three days. We also took a short walk with José to another nearby Inca site, Wiñay Wayna, which is sometimes described as a 'mini Machu Picchu'. The ruins clung to a steep hillside, and the combination of agricultural terraces and triangular-walled houses did bear a certain resemblance to the final stop on our trek.

Day 4: Wiñay Wayna to Machu Picchu

José was determined that we were going to be the first group into Machu Picchu, and to ensure this we were woken up at an ungodly 3 AM. We shuffled down the path, a string of headtorches moving through the dark, as the other campsites were only just beginning to stir. It only took 10 minutes to reach the entrance to the site, where we then had to wait 2½ hours until the park rangers opened the gates. It seemed ridiculous, but we started to appreciate the method to José's madness as the queue of other trekkers grew and grew behind us.

At 5.30 AM the gates opened, and a mad dash to the Sun Gate ensued. We marched along the path, skirting the side of the valley with the river glinting in the sun down below. José had joked about 'one final Gringo Killer' before the Sun Gate, but we still weren't quite prepared for the near vertical steps that confronted us at the end of the trail. It was the only time that we had to use both our hands and feet to scramble up the rocks, and by the time we got to the top I was absolutely drenched with sweat.

But we'd made it to the Sun Gate, one of the first dozen or so people to do so, and down below us there was... clouds. A thick carpet of cloud hugging the base of Huayna Picchu mountain, completely obscuring the famous ruins.

All those bucket list articles you've read are slightly misleading you when they talk about 'watching the sun rise over Machu Picchu'. By the time the gates to Machu Picchu are open the sun is already up, and the site is frequently covered in cloud first thing in the morning. But as we stood at the Sun Gate getting our breath back, the clouds slowly began to move off down the valley, and Machu Picchu was finally revealed to us for the first time.

When you visit a famous tourist attraction that you've seen hundreds of times in photos and on TV, it generally goes one of three ways: it's either a bit disappointing in real life (e.g. the Hollywood sign), it looks more or less how you'd imagined it (e.g. Christ the Redeemer), or it's even more spectacular than you thought it would be (e.g. Iguazu Falls). For me, Machu Picchu definitely fell into the third category; it seems so improbable to have built a city in such a remote and inaccessible location, high up on the side of a mountain.

No one knows for sure why Machu Picchu was built. The American explorer credited with rediscovering Machu Picchu in 1911, Hiram Bingham, believed he had found Vilcabamba, the legendary 'lost city of the Incas'. Vilcabamba was where the last Inca emperor, Manco Inca, established a new capital in the jungle after the Spanish took control of Cusco. But Bingham's theory was later discredited, and the real Vilcabamba was discovered to the west in a place called Espíritu Pampa.

Some archaeologists believe that Machu Picchu was a mountain retreat for the Inca emperors, abandoned when the Spanish invaded. Another explanation for why the Spanish never found Machu Picchu is that it simply wasn't very important, just a remote outpost that held little strategic value.

Whatever its original purpose, Machu Picchu is a fascinating place that showcases the engineering and architectural prowess of the Incas. José showed us the Sun Temple, with its curved walls reminiscent of the Qorikancha in Cusco, and the cave underneath known as the Royal Tomb, where the mummified bodies of Inca nobles may once have lain.

We walked around Machu Picchu's main square, where we saw examples of the Incas' amazing stonework, as well as outcroppings of rock that were never sanded down and polished, suggesting that Machu Picchu may have been abandoned before it was finished. And we climbed up to the altar known as the Intihuatana, the 'hitching post of the sun', topped with a sundial-like rocky protrusion that was used to measure the passing of the seasons.

Although entering the site from the Inca Trail ensures that you're one of the first to get to the ruins, Machu Picchu soon fills up as the coach tours start arriving. By mid-morning we were having to pick our way around Mexican tour groups, selfie stick-wielding Brazilian couples, and geriatric American women with hairstyles last seen in the wild some time during the 1980s. After the relative solitude of the Inca Trail it was strange to suddenly be surrounded by other tourists, though Machu Picchu is big enough that we were still able to find quieter spots to escape the crowds.

There is so much written about the Inca Trail and Machu Picchu online, on blogs and forums and travel websites, and most of it is very subjective. I can't really tell you whether you're fit enough to complete the trek, whether you've bought the right gear, or even which version of the trek to sign up for; what worked for us won't necessarily work for you.

All I can say is that the sleep deprivation, the aching knees and the nightmarish toilets all faded into insignificance when we reached Machu Picchu. The sense of achievement at completing the trek was immense, the scenery along the way was stunning, and hiking the trail brought the world of the Incas to life in a way that no history book or museum exhibit ever could.