The golden lancehead viper is found only on Ilha da Queimada Grande, an island off the Brazilian coast. Photo / 123RF
Thrill-seeking sightseers have found their way to almost every corner of the planet, including some places they probably shouldn't.
But even the most tenacious traveller eventually finds themself being turned back by a gun-toting guard or a skull and crossbones sign ordering Joe Public to venture no further.
A handful of locations around the world are off limits for security reasons or because they're too dangerous while a few are so secret they're officially denied.
According to the South China Morning Post, here are seven places you enter (or try to) at your peril.
Not so long ago, Varosha was a bustling Mediterranean resort known as the French Riviera of Cyprus and favoured by movie stars including Richard Burton, Elizabeth Taylor and Brigitte Bardot. In 1974, Turkish forces invaded the island in response to a Greek-inspired coup and all 40,000 inhabitants fled the holiday hot spot, expecting to return within a few days. They've yet to do so as, 44 years later, Cyprus remains divided.
Today the town is a cross between a modern-day Pompeii and a military no-man's-land. Luxury hotels crumble and decay, homes and cars lie abandoned and the only winner in the conflict appears to be the thriving vegetation. Sturdy mesh fences topped with barbed wire keep curious visitors at arm's length; as do signs warning that photos are forbidden and trespassers risk death.
2. Snake Island
Five times more venomous than the aggressive fer-de-lance snake, which causes more human deaths than any other South American reptile, the golden lancehead viper is found only on Ilha da Queimada Grande, an island off the Brazilian coast.
Local fishermen are reluctant to ferry daredevil day trippers over for a closer look but these days the navy forbids the public from visiting anyway.
Accredited herpetologists can bypass the ban if they get special permission, and presumably a suit of armour. Five thousand snakes, or one every square metre, call the island home and attempts by humans to colonise the lethal land mass have ended badly. A lighthouse keeper and his family died attempting to escape dozens of snakes that slithered in through an open window, and then there was the hungry fisherman who landed in search of bananas, a decision he didn't live to regret.
3, Poveglia
A few minutes from one of the most touristy places on the planet lies one of the most haunted. You can see Venice clearly from the tiny island of Poveglia, which served as a dumping ground for an estimated 160,000 victims of the Bubonic plague. In 1922, the island was converted into an asylum for the mentally ill and patients were soon claiming to have seen the ghosts and heard their tortured screams.
Wish you weren't here? First Venice and Barcelona - anti-tourism protests spread across EuropeWord has it that a doctor who performed lobotomies in the hope of discovering the cause of insanity started to see ghosts as well and promptly jumped to his death from the bell tower. The hospital closed in 1968 and Poveglia is now out of bounds to tourists and uninhabited - by the living at least.
4. Chauvet Cave
Undisturbed by the elements and the hoi polloi since a landslide sealed off the entrance more than 20,000 years ago, Grotte Chauvet, in southern France, has the unusual distinction of being the only Unesco World Heritage Site the public is not allowed to visit.
The cave is protected by security personnel and electronic monitoring systems to prevent a repeat of the damage caused to the 18,000-year-old underground paintings at Lascaux by 2000 visitors a day who introduced heat, humidity and microbes.
As a result, only palaeontologists, speleologists and radio-carbon-dating specialists get to set eyes on Chauvet's 420 paintings and engravings, which are believed to be the oldest anywhere. You could try your luck by turning up in a white lab coat decorated with dinosaurs but I don't fancy your chances of making it past security.
5. Tomb of Qin Shi Huang
After uniting six hostile states and laying the foundations for what would become modern China, Qin Shi Huang set about planning for the afterlife, and there would be no half measures. The warrior, generally acknowledged as the first emperor, died in 210BC and was buried with clay reproductions of his army, family, servants and horses. But while excavations of the terracotta army have been extensive - since its discovery, in 1974, more than 2,000 statues have been unearthed - the nearby mausoleum of Qin Shi Huang remains untouched.
Whether authorities ever allow archaeologists to dig or even survey the tomb is unclear. The warriors were coated in bright paint until exposure to air and sunlight caused them to flake and peel and some argue that existing technology may not be sufficiently advanced for the scale of such a project. Another one to delete from the bucket list.
6. Gaza Tunnels
Israel's decision to restrict the movement of goods into Palestine led to the digging of about 2,500 to 3,000 tunnels under the Israeli and Egyptian borders. The passageways, which were up to 2.5km long and used to smuggle everything from arms and fuel to narcotics and people, have now largely been neutralised by enhanced border fortifications and sophisticated surveillance equipment.
The final death knell was Israel's relaxing of imports to Palestine, which put paid to underground contraband business more effectively than any subterranean technology. Time will tell if any of the remaining tunnels ever open up for tourists to inspect.
Occasionally, sites that have been off limits to the public for years suddenly reopen. Down Street Underground station closed in 1932 but, in 2016, the London Transport Museum began arming groups of 12 with torches and leading them down the 122 steps to platform level as part of a new series of Hidden London tours.
During the second world war, the station was divided into offices and dormitories and used as a bombproof bunker by prime minister Winston Churchill and his cabinet. Market forces based on the British obsession with all things war-related mean tickets cost an eye watering £85.50 ($163) for the 90-minute tour.