Tonto nudges my hip as I grip him, with numb knuckles, to my side. He's all geared up and raring for me to get on with the downhill ride. We're standing 4910m above sea level - 1100m higher than Mt Cook - on the edge of the highest pass of the world's second deepest canyon.
I've never been at such high altitude before. I hate heights, I'm no downhill demon and my breathing feels strangely shallow. My only positive thought is about the hidden benefits of wearing tight, padded lycra pants.
"You've got switchbacks for 31 km from here down to Chivay. Use both brakes, but don't keep them on all the time or they'll burn out," beams Rudy, our guide. "And keep your distance."
Friends doubted our sanity when I signed up for a 12-day cycling tour of Peru, the first run by Kiwi Louise Vargaya-Conza and her Peruvian husband, Rudy, both experienced guides, who are tapping into the growing market for biking adventure tours there.
Based for half the year in Rudy's home town of Arequipa, they run their Cycle Peru tours during the country's sunny, dry winter when day temperatures in the southeast average around 26C and the mercury drops to an average 3 or 4C at night.
Tonto is my mountain bike, one of Cycle Peru's grunty new Specialized Hardrocks which our 13-strong group will ride through some of the planet's most extreme landscapes.
With our bodies fortified with traces of rabies, typhoid and tetanus as well as Diamox, a sulphur-based antibiotic that can help prevent altitude sickness, we will ride in the breathtaking Colca Canyon, past pink pelicans on the Peruvian Altiplano, the earth's highest plateau outside Tibet, and through the Sacred Valley of the Incas.
Mid-tour we'll boat from Puno across Lake Titicaca, the world's highest navigable lake, to step back in time and stay with locals on Amantami Island. Then after three days of hardcore cycling we'll wind up our tour poking around the fabled Incan citadel of Macchu Picchu and its nearby town of Aguas Calientes.
Anarchy is the only way to describe the traffic as we drive into Arequipa from the airport, eyed by the indolent peaks of Picchu Picchu, Chachani and El Misti.
These godly landmarks encircle Peru's second largest city, keeping a distant watch over its creeping suburbs and sillar-stoned, white heart.
Like its traffic, head-strong Arequipa is hurtling along, making the most of its accelerating tourism boom and helping Peru hold its place as one of the world's fastest growing economies.
The traffic bothers me, but we have two days to acclimatise at 2300m before getting on our bikes. Our first two cycling days are around the outskirts of Arequipa, about 20km a day, to keep acclimatising, get to know our bikes and the others on the tour.
Aged between 36 and 69, we come in all shapes, sizes and levels of fitness. Retired couple Bob and Carol ride tandem back home in Massachusetts, and old mates Kerry and Danielle from Melbourne and Townsville are on a girls' trip of a lifetime.
Dutch-born Baz, a trained Audi mechanic who switched to bikes and worked for the Tour de France for a few years, has biked in more than 90 countries. Baz and friend Bea are celebrating her 70th by doing a 600km, extreme cycling tour of Bolivia and Chile when our one ends.
Our tour is carefully planned so we "climb high and sleep low" and don't usually ascend more than 1000m a day. There is no pressure to compete. When you want a break you can jump into the support vehicle, and routes are planned to avoid heavy traffic.
Day three's 31km downhill cruise from 4910m at Patapampa Pass to Chivay, on the upper Colca River, is the first real challenge. The van trip from Arequipa to Patapampa is a 1200m ascent.
Within minutes of starting to ride on the sealed road the views are so intoxicating I'm too overcome to stay scared. Pre-Incan terraces still cultivated by the local Collagua and Cabana people stack like neat lines of lego into the canyon walls and giant condors soar on warm air currents that rise from the fertile valley floor.
After barrelling downhill for more than 90 minutes, I round a switchback and am struck by a mosaic of iridescent colour glinting in the sun against the Colca's gargantuan, grey rocks: local women in intricately embroidered brilliantly dyed traditional clothes and Cabana hats are selling their handicrafts on the side of the road. One magic moment in what is becoming the most invigorating, stimulating trip of my life.
That night in Cabanaconde, a nagging altitude headache keeps me from my pisco sour. After a deep sleep and surreal dreams I wake clear-headed and ready to chew up 17km of deeply corrugated, downhill gravel roads, then have the energy after lunch for 20km uphill slog before slipping into hot pools beside the ice-cold Colca River at our El Refugio hotel.
Ripping along at 4300m over the wetlands of Toccrapampa - 17km in 37 minutes - day five's ride is a frosty, mind-blowing blast before we retreat to the van with the bikes in tow for a four-hour ride to Puno on the shores of Lake Titicaca.
About 40 minutes out of Puno, we pass through Juliaca, the main transit point for thousands of dollars worth of contraband that passes between the Peruvian and Bolivian borders each week. Grain, gas bottles, stolen cars, microwaves, you can get it all in Juliaca. Just watch the shoes on your feet.
Wary because I've heard homestays on Lake Titicaca's islands line the pockets of Puno agents who arrange them and rip off the locals, I'm relieved to learn the families we will stay with on Amantami will be properly paid. It's one more example of how Cycle Peru walk their talk of offering ethical and sustainable tours.
After three days off our bikes, then a six-hour van ride from Puno to the Incan capital of Cusco, we are itching to ride again - up to 90km on day nine.
From the hills above Cusco, we do a steep, 8km climb to a lookout over the amphitheatre-like ruins and agricultural terraces of the Sacred Valley. Then it's an 18km descent whizzing past waterfalls, adobe villages and ochre farmland down into the narrow, winding Rio Urubamba Valley.
A 15km flat run from the market town of Pisac takes us alongside the Urubamba River where we stop for a picnic lunch before a 15km run to Yanay then a final 20km haul to Ollantaytambo , the last Incan town to capitulate to the Spanish after holding them at bay for 38 years until 1574.
Out of bed early the next day, we climb more than 200 terrace steps to the top of Ollantaytambo's Temple Hill fortress which was built as the royal estate of Incan emperor Pachacuti. A stupendous feat of engineering that took about 7000 people more than 65 years to build, the temple is testimony to the Incans' advanced astrological and agricultural knowledge and a foretaste of what we'll see at Macchu Picchu.
If I'd seen our final two cycling routes on day one, I wouldn't have left the van. From the 4315m-high Abra Malaga Pass in the shadow of Mt Veronica, we jack-knife down a slithering sealed vein that dissects the sheer drops below it. Over four hours, we ride more than 75km and descend a heady 3000m - the last part a mud-spattered, rough-as-guts rollick through 35km of road works, rubble, landslips and fords to the isolated, high jungle town of Santa Maria. At our hotel in Quillabamba it takes twice as long as usual to scrub off the dirt from the day's ride - but nothing is going to wipe away our adrenalin-fuelled smiles.
Deborah Telford paid for her own flights and was a guest of Cycle Peru.
* Best months for cycling in Peru are May to September. The tour that I went on cost US$2295 per person based on a twin share. You can also do shorter tours - our friends joined us half way through and that cost them US$1495.
Top 5 in Peru
Flight Centre's Sian Sherriff recently travelled to Peru and shares her top five must-dos:
1. Machu Picchu is not to be missed. The area's history, the mountains and the jungle add to mystery of the Inca ruins.
2. The Lares Trail is a fabulous alternative to the Inca Trail. With no stairs and shorter days, it is easier, however the trek reaches a higher altitude. Walk through farmland, stay in local villages and meet the people.
3. Try the local cuisine - Peruvians love their food. They like it flavourful and in big portions - you will never go hungry. Be adventurous, try empanadas (small pies), cooked alpaca or guinea pig and one or two of the 9500 known varieties of potato. There is a local dish to suit every taste and budget.
4. Visit the Amazon jungle from Puerto Maldonado. I suggest staying at an eco-lodge and walking through the jungle to see the exotic wildlife up close.
5. Wander the streets and explore the local markets in the picturesque city of Cuzco. This is a great opportunity to visit the nearby ruins of Saqsaywaman, the Sacred Valley and the Pisac Market.
For more information on Peru, contact Sian Sherriff at Flight Centre on 0800 427 555.