SEE ALSO: 26 places you should visit before they disappear forever
FOLLOW US: INSIDER Travel is on Facebook
The Tropical Rainforest Heritage of Sumatra, located on the Indonesian island of Sumatra, is home to many endangered and diverse species but was added to the UNESCO List of World Heritage in Danger in 2011.
According to UNESCO, the Tropical Rainforest Heritage of Sumatra consists of three distinct national parks and has 10,000 plant species, 580 bird species, and 200 mammal species, including the Sumatran orangutan.
Protecting the site means protecting those species as well.
Liverpool helped the British Empire grow into what it was in its heyday.
The port was added to UNESCO's List of World Heritage in Danger in 2012.
According to UNESCO, the World Heritage Committee requested the current buildings remain the tallest in the city.
However, urban development and an increasing population threaten to permanently change the port.
The Florida Everglades has a huge amount of biodiversity and is an important natural site.
UNESCO added the Everglades to its List of World Heritage in Danger in 1993 because of damage caused by Hurricane Andrew. In 2007, conservation efforts got it removed from the list.
In 2010, the Everglades were put back on the list.
The site also houses quite a few endangered species, further increasing its importance according to UNESCO. Unfortunately, environmental degradation and development threaten the site.
Coro, Venezuela, and its port were added to the UNESCO List of World Heritage in Danger in 2005.
According to UNESCO, the city is the only surviving example of a rich fusion of local traditions with Spanish Mudéjar and Dutch architectural techniques.
The area and its species have been dealing with a lot of pollution from the Venezuelan oil industry, according to Bloomberg.
The beautiful port city is one of the oldest colonial towns in the region, according to Smithsonian magazine.
The historic center of Vienna was added to UNESCO's List of World Heritage in Danger in 2017.
There's a chance that the historic center of the city will be irreversibly changed because of modernization and urban development, according to UNESCO.
With the increase of high-rise developments, the site — known as the center of European music and art — is losing its history.
The Belize Barrier Reef System, which was added to the UNESCO List of World Heritage in Danger in 2009, is the largest barrier reef in the northern hemisphere, according to UNESCO.
Belize's coast — and the Belize Barrier Reef System — is home to many vulnerable, important, and diverse species.
Protecting the reef means protecting threatened marine life.
The Old City of Jerusalem and its walls were added to the UNESCO List of World Heritage in Danger in 1982 after Jordan suggested that the organization add the site.
Jerusalem is a sacred site in Judaism, Christianity, and Islam, and, according to UNESCO, contains 220 historical monuments.
Due to urban development and city planning, a lack of protection, and other issues, this site is considered endangered, according to UNESCO.
There's still controversy regarding its cultural value and how it's treated, according to The Guardian.
Various reconstruction and preservation projects have been underway, however, with the Antiquities Authority and The Jerusalem Foundation conducting work, culture minister Miri Regev announced plans in late 2017 to preserve and develop historical sites.
This Bolivian city was added to the UNESCO List of World Heritage in Danger in 2014. The city showcases a blend of Spanish and native cultures.
According to The Guardian, the silver mine in the city was formerly thought to be the largest one in the entire world until its demise.
However, because of the increase in mining, the town's actual foundation is in serious trouble.
If you've never seen a glacier, you might need to make a trip to Glacier National Park in the immediate future.
According to National Parks, the park used to include over 150 glaciers, but that number is now down to 25.
Depending on how quickly climate change progresses, the number could continue to decrease rapidly, according to the National Park Service.
According to Discover Peru, Chan Chan was the capital city of the Chimu Kingdom, who ruled in Peru before the Incas took over. It was added to UNESCO's List of World Heritage in Danger in 1986.
Chan Chan was thoughtfully and intricately planned with irrigation systems, until Spanish miners pillaged the city and extreme storms caused further damage, reported by Smithsonian magazine.
According to UNESCO, illegal farming is taking place in the area and the structures themselves aren't protected from the area's weather, so the ancient city is in further danger of destruction.
Like the Maldives, Seychelles — a group of islands in the Indian Ocean — is also dealing with beach erosion, according to Coastal Care.
However, their government has made strides and created nature preserves and marine parks to conserve the island biodiversity, according to Britannica.
Nevertheless, if you want to experience these island oases, time might be of the essence.
World Heritage Sites noted that the ancient city of Abu Mena was built in A.D. 296. Its structures are primarily built in clay, according to UNESCO.
It was added to UNESCO's List of World Heritage in Danger in 2001 because the foundations of the buildings are softening due to higher water levels.
The Selous Game Reserve was added to UNESCO's List of World Heritage in Danger in 2014.
According to UNESCO, much of the reserve has generally remained untouched by humans. A wide variety of animals ranging from elephants to rhinoceroses to cheetahs, giraffes, and more, all call the game reserve home.
The Frankfurt Zoological Society reported that Selous also contains numerous kinds of vegetation, from swamplands to woodlands and grasslands.
It's one of the biggest areas of protected wildland in Africa.
Kosovo boasts plenty of medieval architecture, however, those structures endured quite a bit during the unrest in the Balkans in the 1990s, according to Endangered Sites.
The churches and monasteries in the region contain Balkan art from the 13th to 17th centuries and still need more work after the war.
These islands — known as the lowest-lying country on Earth— are susceptible to rising sea levels, meaning they are in danger.
According to NASA's World Observatory, the Maldives — which only sit less than one meter above sea level — could potentially be completely submerged within the next 100 years if water levels keep rising.
The Maldives is trying to reduce carbon emissions by 2030 to minimize the impact of climate change, according to CNBC.
