21 World Heritage Sites You Should Visit Before They’re Lost Forever

In Vienna, UNESCO thinks there's a danger that high-rise projects are ruining the historic skyline of this great city. Here on the Danube River, visitors come for its musical legacy (it was home to Mozart and Beethoven), its Imperial palaces such as Schönbrunn, its Baroque castles and gardens, and its Habsburg architecture. What this grand city of cobbled streets doesn't seem to need is luxury apartments, a skating rink and soaring hotels.

Combine this biosphere reserve with others in Honduras and neighboring Nicaraguan, and you’ve got the largest area of forest in Latin America north of the Amazon. We’re talking dense rain-forested mountains, wetlands, savannah and coastal lagoons. There are indigenous peoples here, petroglyphs, and scores of endangered animals. The critically endangered Mexican spider monkey, tapir, giant anteater, West Indian manatee and jaguar can all seen here, as well as giant turtles and more than 400 species of birds.

With fewer than 15,000 of the animals left in the wild, the critically endangered Sumatran orangutan is on the brink. The so-called “old man of the forest” used to exist over the entire island of Sumatra, and even into Java, though now only nine small populations remain. Worse than that, only seven appear to have prospects of long-term viability, and each have fewer than 250 members. UNESCO thinks that Sumatra's three national parks — Gunung Leuser, Kerinci Seblat and Bukit Barisan Selatan — represent the greatest potential for long-term conservation. Visit any of these three, and you might also see elephants, rhinos and tigers.

Just 90 minutes drive south of Samarkand is Shakhrisyabz, a 2,000-year-old city of the Kesh region. Here you'll find medieval walls and blue domed mosques, but there's more of a mix of architectural styles that than in Samarkand. It's under pressure from over-development of tourist infrastructure.

This landlocked country in the Balkans only declared independence from Serbia in 2008, and yet it contains some incredible churches and monasteries. If ecclesiastical excursions are your thing then you'll want to visit these four examples of Byzantine-Romanesque wall painting, which developed in the Balkans between the 13th and 17th centuries. However, the Dečani Monastery, Patriarchate of Peć Monastery, Church of Holy Apostles and the church of the Holy Virgin of Ljevisa are threatened by the region's political instability.

About 500 years ago, this small town high in the Bolivian Andes became an industrial powerhouse that changed the global economy. It was the 16th century, and the Spanish conquistadors had found silver in the New World. You can still see the remains of the massive industrial complex at Cerro Rico, from the mines, aqueducts and industrial monuments to the Royal Mint, the workers' homes and the Church of San Lorenzo. Sadly, Cerro Rico’s summit is in danger of collapse.

East Africa gets the tourist dollars when it comes to safari, but there are other options. The banks of the Gambia river in this French-speaking country in West Africa, Niokolo-Koba National Park contains elands, chimpanzees, lions, leopards and elephants. It's under threat from poaching of elephants, and also from plans to construct a dam on the Gambia river just upstream, which would prevent the grasslands of the site from flooding. UNESCO wants the Senegalese government to step-in.

The nearby Bwindi Impenetrable Forest is where most visitors head after arriving in Uganda's capital, Kampala, but there's a good reason to hang about. On a hilltop in the city's west are the dramatic Tombs of Buganda Kings at Kasubi, built in 1882 and converted into the royal burial ground in 1884. Built from wooden poles, thatch, reed, wattle and daub, the main building of this major spiritual centre for the royal family was gutted by fire in 2010.

UNESCO estimates that 62 of its World Heritage Sites are threatened by climate change, and none more so than East Rennell in Rennell Island, the southernmost island of the Solomon Islands in the Western Pacific. The largest raised coral atoll in the world — at 86 kilometers long and 15 kilometers wide — rising lake water levels from climate change are adversely affecting some staple food crops of the resident Polynesian villagers. So too are the area’s now more frequent cyclones.

Ghost towns don't usually last long, but in the remote Pampa, one of the driest deserts on the planet, this one could live forever if it wasn't for regular and devastating earthquakes. The world's biggest reserve of potassium nitrate, also called saltpeter, was mined here by thousands of people from the first half of the 19th century. Why? To produce the fertilizer sodium nitrate that transformed the productivity of agricultural land in the Americas and Europe. There are over 200 now-derelict and quickly crumbling saltpeter works here.

Madagascar and its animals are unique, having split from other land masses over 60 million years ago and evolved in isolation. It's now been seven years since this last bastion of rare and threatened primates and lemurs was placed on UNESCO's watch-list. Atsinanana comprises six national parks along the eastern part of the island, and protect the oldest rainforest of Madagascar. Sadly, the area is threatened by illegal timber logging of rosewood and ebony.

Want to see a manatee? Go now. On the list since 1979 – and danger list now for seven years – Florida's Everglades are suffering from lowering water levels due to urban and agricultural growth, and pollution from agricultural activities, resulting in a decline in marine species – including the manatee.

This enormous and relatively undisturbed game reserve in southeast Tanzania is where enlightened tour operators send their guests. Away from the bustle of safari jeeps in the more popular Serengeti and Ngorogoro Crater, you can see elephant, cheetah, giraffe, hippopotamuses, leopard and the little-known Selous lion, which have smaller manes than others in Tanzania. However, rampant poaching has caused a dramatic decline in the wildlife populations, especially of elephant and rhino.

A reputation for being at the end of the road has kept Timbuktu part of traveler lore for centuries, but in recent years this “city of gold” on the edge of the Sahara desert has come under severe threat. Its three dramatic earthen mosques of Djingareyber, Sankore and Sidi Yawhia are what tourists come to see. Or, at least they did until 2012's 10-month occupation of Timbuktu by Tuareg separatist rebels, then jihadists. However, the mosques were already under threat from desertification due to drought and overgrazing; the mosques are literally crumbling into dust.

Venezuela is a country in crisis, and not likely to attract many tourists. That's a shame because on the Caribbean coast in the state of Falcón you'll find the small town of Coro, which has buildings of earthen construction dating back to 1527 that have a unique fusion of local traditions with Spanish Mudéjar and Dutch architectural techniques. Close to the Coro Dunes National Park, it's a photographer's dream, but for how long? Coro was badly damaged by unusually heavy rains in 2005, and has since lacked a management plan to restore and protect it.

This one must have been on UNESCO's World Heritage list since the beginning, right? actually, the Church of the Nativity was the first property in Palestine to be inscribed on the list as recently as 2012. You'll find the remains of St Helena church built in the fourth century, and another over it from the sixth century (Church of the Nativity). It’s their association with the birth of Jesus makes it a holy symbol for both Christians and Muslims. There's a cave over which the first church was built that’s believed to be the birthplace itself. However, it's threatened by urban pressure, tourism and traffic management, so make your visit a short one.

Seen Machu Picchu? Now go see Chan Chan. The largest earthen city in pre-Columbian America, the remains of this vast city on the Pacific coast of northwest Peru is something to behold. In its heyday about 600 years ago as the largest city in the Americas — population 60,000 — Chan Chan was the capital of the Chimu Kingdom. Thick earthen walls separate nine distinct citadels, each with temples, homes and funeral platforms within. It was deserted because of a shortage of water, but now regular torrential rains are slowly washing it away.

Egypt is just about pyramids and temples, right? Actually, many events in the Bible took place in Egypt, and 28 miles from the great city of Alexandria is this Christian pilgrimage centre built over the tomb of the martyr Menas of Alexandria, who died in A.D. 296. Still standing are the remains of the church, baptistry, basilicas, public buildings, streets, monasteries, houses and workshops, but for how long? Abandoned a Millenia ago, the site is threatened by a rising water table, which could lead to flooding and further collapse.

Have you even heard of Africa's largest protected area? This area of Niger, a landlocked country in Western Africa, is entirely surrounded by the Sahara desert. Within our moving sand dunes, blue marble mountains, and some of the last populations of three antelopes of the Sahara Desert on IUCN's Red List of threatened species; the dorcus gazelle, the leptocere gazelle and the addax (screwhorn antelope). There are also cheetah living here. However, poaching and illegal grazing have been threats since 1992, and it’s getting worse.

It may be most famous for spawning The Beatles, but the city of Liverpool played a big role in the growth of the British Empire. It became a major port for the mass movement of people, including slaves and emigrants from northern Europe to America. Much like Vienna, UNESCO fears that new, modern developments will overshadow its historical buildings and structures, specifically its historic docklands. Its sympathetically redeveloped, UNESCO-protected Albert Dock is home to the International Slavery Museum and, on a happier note, The Beatles Story.

Part of the longest barrier reef in the Western Hemisphere, and Belize's top tourist attraction for snorkeling and scuba diving, Belize Barrier Reef is a vast area of offshore atolls, sand cays, mangrove forests, coastal lagoons and estuaries. It's home to marine turtles, manatees and the American marine crocodile. It's most famous feature is the Great Blue Hole sinkhole, but the entire area is threatened by development on its mangrove islands. However, there's a plan underway to conserve the area, and the government has just banned offshore oil exploration.