Yet regulations imposed by the Peruvian authorities limiting numbers to 500 people starting the trail each day mean that this is the lowest number of people on the trail for a decade.

Of those 500 trekkers, nearly two-thirds are actually guides, cooks and porters employed to carry tents, provisions and cooking equipment. The regulations also mean that only licensed tour operators are allowed to take groups on the four-day trail and independent hiking is no longer an option.

The result is that the Inca Trail gets booked up pretty quickly and international tour operators and Peruvian travel agencies are having to look at alternative walking routes in and around the Sacred Valley.

Tours to the rarely visited vast archaeological complex at Choquequirao, to Peru's most revered peak Ausangate and to the remote Lares Valley are becoming increasingly popular, particularly as they can be booked at a few days' notice upon arrival in Cusco.

According to Lucy Bertenshaw, manager of the South American Explorers Club in Cusco: "It's important to maintain the present permit system on the Inca Trail as it aims to limit the damage that heavy foot-traffic can do. If you're after a pristine wilderness experience, the Inca Trail probably doesn't offer that any more but there are plenty of other trails in the area that do."

The Inka Porter Project, a not-for-profit organisation that campaigns for better working conditions for Andean porters and animal drivers as well as improved environmental practice in the region, is concerned that directing tourists towards unregulated trails will have a negative impact on delicate ecosystems.

Louise Norton, director of the project, said: "Expanding tourism can bring great benefits but it must be done in a responsible way. We don't want the same thing that happened with the Inca Trail a few years ago where people were using the ruins as toilets and chucking away rubbish indiscriminately happening again elsewhere." With this in mind, the Inka Porter Project has published a set of guidelines for trekkers that contain advice on keeping contamination of the environment to a minimum

If steps have been taken to preserve the Inca Trail, it's a very different story when it comes to the Unesco World Heritage Site of Machu Picchu. Mike Weston, owner of local travel agency PeruTreks, says: "The Peruvian authorities should be praised for their progressive stance on successfully protecting the Inca Trail for future generations - we only wish they would do the same for Machu Picchu itself, which currently has no restrictions on the numbers allowed to enter the ruins".

Last year, Unesco threatened to place South America's most visited historic monument on its list of endangered cultural heritage sites. Uncontrolled tourism has led to considerable erosion of the incomparable ancient city as well as ugly and badly planned development in the satellite town of Aguas Calientes.

The "Lost City of the Incas" generates something in the region of £22 million a year for Peru's economy so it's little wonder that the country's National Institute of Culture has rolled out a £70 million, 10-year master plan to conserve the ruins.

Proposed measures include limiting the number of daily visitors to 2,500, increasing the admission fee and satellite monitoring of the earth's movements in an area prone to landslides.

Added to the World Heritage List in 1983, Machu Picchu receives around 300,000 people a year compared to 180,000 in the mid 1980s. Its fate should be known in the second or third week of July when Unesco's World Heritage Committee meets in Durban to decide the status of endangered sites.

American tourist Anneliese Sherfen has just visited Machu Picchu and thinks that capping the number of visitors can only be a good thing: "We did the Inca Trail, so arrived early in the morning and had the site to ourselves - but then the first tour buses started to arrive and there were hordes of people swarming all over like insects. You could almost sense the destruction taking place."

With tourism to Peru very much on the increase, it's estimated that visitor figures to Machu Picchu could rise to as many 5,000 people per day in the next few years. Ironically, the only major Inca site to escape 400 years of looting and devastation is now at risk from modern-day marauders armed with cameras and sweaty palms which leave harmful salt deposits on some of the finest stonework the world has ever seen.

Times recommends

• New York's top 10 new hotels
• A Scottish monastery retreat
• Welcome back to Rwanda