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Mankind has built stunning landmarks that have stood the test of time.

While preservation efforts by UNESCO and other groups are ongoing to keep these sites from deteriorating, wear and tear and the very people that come to admire their beauty have become their greatest enemies.

Some places have tried capping visitor numbers, others shut down seasonally --but all fight for funding to keep things running.

Here are some of the world’s most famous landmarks in desperate need of restoration.

1. Angkor Wat – Siem Reap, Cambodia

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(Reuters)

From butt-baring tourists to thieves selling off relics, the ruins of Cambodia’s majestic temple complex have suffered over the years. The site has been exploding as a tourist destination each year—according to UNESCO over 800,000 people visit the sacred site annually.  But the ancient site is being strained by influx of foot traffic. Restoration efforts have been ongoing.  China recently stepping in with satellite technology to monitor environmental factors that are contributing to the site’s degradation. Numerous reviews on TripAdvisor have sited major repairs limiting access to certain portions of the temple but still note that it’s a wonderful place to visit.

2. Caves of Altamira - Santillana del Mar in Cantabria, Spain

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(AP)

The drawings at this UNESCO World Heritage site date back to the Paleolithic age making them some of the earliest known artworks known to man. Spanning throughout 17 different caves, the drawings depict wild animals like bison and deer and human hands. It might be expected that after 20,000 years, the usual wear and tear would begin to effect the quality of the paintings. In 2002, the Spanish government closed the site to the general public. Today, the nearby museum draws big crowds, and once a week, five lucky visitors are chosen at random to don protective gear and visit a selected area of the cave for 37 minutes.

3. The Great Wall of China

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(Reuters)

The only man-made structure visible from space, the Great Wall of China is arguably one of mankind’s most impressive structures ever built. At one point the wall stretched over 13,000 miles, but today it is disappearing.  According to state media in China, about 30 percent of the wall has eroded over time due to natural wear like overgrown plants and weather, as well as from vandals stealing bricks or destroying the structure. Construction on the Great Wall dates back to third century BC, but the majority of the wall was built during the Ming Dynasty (1368 – 1644). Over the years, local villagers have taken bricks from the wall to build homes or tried to sell parts of the wall to tourists, though the practice is illegal and can result in fines. An increase in tourism to lesser-protected areas of the wall has only heightened the damage. According to some reports, the government is working with local municipalities on plans to restore and protect the Wall’s rural sections.

4. Spanish Steps – Rome, Italy

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(Reuters)

Built in the 18th century, these iconic steps connect the Piazza di Spagna at the base and the Piazza Trinità dei Monti in Rome. Featured in classic movies like “Roman Holiday” and “The Talented Mr. Ripley,” the steps are a popular attraction for tourists and locals. But the years of constant stepping have taken their toll.  Cracks have appeared on the stone surface from both people and invasive plants jutting through.  Also, loose stones and deep stains mare the site. The steps were last restored in 1995 but earlier this year Italian luxury jeweler Bulgari announced that it would be donating 1.5 million euros to restore the site. The steps are now closed to foot traffic but a partial section is slated to reopen Dec. 7.

5. Big Ben – London, England

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(Reuters)

This iconic clock that's adjoined to the Britain's House of Parliament may be running out of time. According to a new report, the 9-foot-long hour hand and 14-foot-long hands of Big Ben’s could break off and crash to the ground without immediate repairs. Parliament has proposed a $45.1 million restoration plan that would keep the clock out of commission for about four months—the longest suspension of timekeeping in the Great Bell Tower’s history. No date has been set for repairs to begin.

6. Venice, Italy

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(Reuters)

Venice is sinking. But how fast has been the subject of great debate. The city has experienced increased incidents of flooding throughout the past decade and local officials have tried to protect the historic sites—without deterring the thousands of tourists that keep the city afloat financially. To the disappointment of celebrities like Cate Blanchett and Michael Douglas, the city overturned a large cruise ship ban last year. If you’re planning a trip to Venice soon, check out information on historic sites that may be closed for restoration during your stay at Venice in Peril. One thing is clear, if you want to make a trip to this iconic Italian city, don’t wait too long.