They are holidays billed as an opportunity to enter another world, a chance to see the world's last primitive tribes up close in their natural environment.
The brochures tease and at times, critics say, titillate. Take the Delhi-based Aces Indian Tours, which invites visitors to travel to see the Bonda people, an ancient tribe found in the remote hilly regions of the state of Orissa.
The website breathily offers to provide an insight into utterly different lives.
"On the northwest of river Machkund", it states, "live the wildest, rudest and possibly the most interesting tribe known as Bonda Tribe. The scanty dress of the Bonda women and homicidal tendency of Bonda males make them most fascinating people."
It is this kind of exotic invitation that has now come under unprecedented scrutiny in India, raising ethical issues that also apply to similar tours in other remote regions of the world.
Every year, thousands of Western tourists visit India in search of the exotic. But two weeks after an Observer investigation exposed the degradation of "human safaris" in the Andaman Islands - which are in Indian territory - the country's travel industry has entered a bout of soul-searching.
Video evidence that Jarawa tribeswomen had been bullied into dancing for convoys of visitors on the islands' main road sparked a furious reaction.
Sonia Gandhi, leader of the ruling Congress party, has taken a personal interest in the 400-strong Jarawa's fate and is understood to be frustrated by the lack of action to protect them.
At a meeting last week of the powerful National Advisory Council, which she chairs, members denounced the "deplorable situation of the exploitation of the Jarawa tribe".
The investigation has now prompted the Home Minister, P. Chidambaram, to demand the interrogation of those responsible. Last week he flew into the Andamans to tell officials there to act swiftly to prevent further abuse of the tribe.
Tribal Affairs Minister V. Kishore Chandra Deo said: "It's deplorable. You cannot treat human beings like beasts for the sake of money. Whatever kind of tourism is that? I totally disapprove and it is being banned."
But what about elsewhere in India, and in other parts of the world? In the case of the Jarawa, there is little doubt that the tribespeople have been exploited by unscrupulous locals and insensitive visitors.
Elsewhere, ethical lines are usually more blurred, but the risk of damaging contact with vulnerable communities is very real.
In 1989, India introduced the Scheduled Caste and Scheduled Tribe (Prevention of Atrocities) Act in an attempt to protect indigenous communities from "indignities, humiliations and harassment".
But with the number of tourists across the world expected to hit a billion this year, and previously inaccessible places beginning to open up for more and more people, how close should travellers be allowed to come to vulnerable communities?
One of the most popular destinations in India is Orissa, where tour operators promise sightings of the insular Bonda when the tribespeople leave their homes to go to a market in the village of Onkadeli.
Entry into the Bonda's own villages is illegal: the tribe do not invite attention and many dislike being photographed, but the market offers a way to view them, and the tours continue.
Even the state tourist board uses images of the tribe in its adverts.
Royal India Holidays, with offices in India and the United States, offers a tribal tour of Orissa where it promises tourists can "see the lifestyle of tattooed, heavily beaded, nearly naked tribal people, their day to day activity and their extremely primitive way of living".
The company says it is recognised by India's ministry of tourism. Its brochure describes a trip to the Jeypore area of Orissa: "After breakfast, an excursion to the nearby hills where most amazing and fierce Bondas Tribes [naked people] reside. They are also known as Remo meaning 'people'. The Bonda are generally semi-clothed, with the women characterised by the wearing of thick silver necklace bands.
"The tribe is one of the oldest and most primitive with their culture little changed in over 1000 years. The best way to view members of the tribe is by going to local markets held every Thursday."
Company owner Newton Singh said that most tours in Orissa focused on the tribes. He said he believed that the company was operating within the law but it relied on local agents in Orissa.
He said he understood the objections and would review the tours.
"I don't want to do anything against the laws of humanity," he said.
Survival International, which campaigns on behalf of tribal peoples, is sceptical that such a high-minded approach is reflected by what takes place on the ground. The charity's director Stephen Corry said: "We are now in the 21st century, not the 19th. Colonialism should be a thing of the past. Tribes are not cultural relics, nor should they be treated like animals in a zoo.
"They are not ancient or backward, but adapting like everybody around us to a changing world. This should entitle them to the same rights and freedoms as the very tourists who are taking their photographs.
"Promoting tours by using derogatory terms such as 'primitive', and advertising their 'nakedness' shows a clear lack of respect."
Corry said tour operators had no right to promote tribal people as a tourist attraction. "Forcing them to dance in return for sweets and biscuits, for the amusement of onlookers, is only possible where they're viewed as somehow less than fully human," he said.
"Sadly, the existence of human safaris in the Andamans is not isolated, but replicated in other areas of India. It is crucial tourists boycott such unethical 'attractions', so there is no fuel in the market to drive such tasteless practices."
Association of British Travel Agents spokesman Sean Tipton said the travel industry recognised the necessity of regulating and monitoring interaction between tourists and tribes.
"Customers should always seek permission before taking photographs of indigenous people, or indeed any local people. This is a matter of courtesy and cross-cultural sensitivity."
Clearly, though, more needs to be done. British travel firm Audley Travel, winner of three Guardian Observer Travel Awards, offers tours to Orissa in which it promises sightings of the Bonda tribe, despite acknowledging that photographing them may be banned.
The company said it firmly advocated responsible tourism and only took individuals or couples.
"They are accompanied by tour guides who are well briefed on the cultural sensitivity of the situation, particularly photography."
In the Andaman Islands, police say they have made some progress in identifying those responsible for filming the video publicised by the Observer, which is now believed to have been shot in September or October of 2008.
The Lieutenant Governor of the Andaman and Nicobar Islands, Bhopinder Singh, has been ordered to take action to prevent further exploitation of the Jarawa.
Trips to do, or not
* The Andaman Trunk Road, Andaman Islands, Indian Ocean. Tour operators take thousands of tourists to "spot" members of the tiny Jarawa tribe, which could be devastated by an epidemic.
* Kalahari Plains Camp, Central Kalahari Game Reserve, Botswana. Owned by Wilderness Safaris, built without consulting local bushmen, on whose ancestral lands the lodge sits.
* "First contact" expeditions, West Papua, Indonesia. Treks to an area where tribes "have had no contact with the outside world".
* Wayo Africa, Tanzania. Guided visits to the Hadzabe create funds for various projects.
* Kapawi Lodge, Ecuador. Lies in land of the Achuar people. Small groups are led by a bilingual guide and a native Achuar guide.
* Aboriginal Cultural Tours, Yorke Peninsula, Australia. Ecologically and culturally sensitive excursions.
Source: Survival International