The world is a beautiful place. From small USA towns, to massive European cities, to the far reaches of the most desolate corners, there’s beauty to be found wherever you go. But that doesn’t always mean that the beautiful places are welcoming for visitors from the United States of America.

Travel advisories are put into place by authorities to help keep the people of America safe when traveling. While there might be some circumstances that actually do allow USA folk to visit these places, they are often extremely complex or require very specific criteria. Numerous places are listed as a level 4 warning or a stricter do not travel zone for US citizens. Plus, some nations have their own restrictions on whether or not people from America can visit.

Before planning your next adventure, take a look at this list to double-check if, firstly, you're actually allowed to cross the border as a foreigner, and secondly, if it's a good idea (or a totally ridiculous and unsafe idea) to do so.

20 Mogadishu, Somalia - Classic Italian Architecture and Coastlines

Mogadishu is the capital of Somalia and a beautiful coastal city. With beaches stretching along the perimeter, the city was an important port for centuries and adopted various aspects of the different cultures that frequently passed through it. The classic Italian-inspired architecture found around the city is a compliment to Lido beach. Visitors often enjoy boating excursions to enjoy the ocean views.

Because of dangerous conditions in the country, travel is restricted for USA folk wishing to experience the city. Even when travel is allowed, very few hotels actually accept international visitors, complicating accommodations even more.

19 Port-Au-Prince, Haiti - A Gem of the Carribbean

Port-au-Prince is a city that's most famous for its busy ports of times long past. But much of the beauty still remains in the colorful buildings and culture. Haiti has been an independent country since 1804, but much of the French inspiration still lingers in the architecture, especially in the heart of the city.

The city also has a vibrant and unique music scene. British musician Mark Mulholland told The Telegraph that, "what often fails to reach the attention of the outside world is the richness of the culture and history of Haiti and its people, as well as the spectacular beauty of the country itself."

Unfortunately, the US government banned all unofficial travel to the southern peninsula of the country following Hurricane Mathew.

18 Sana'a, Yemen - Ancient History Brought to Life

Sana'a is the largest city in Yemen and is full of beautiful, ancient buildings. The Old City of Sana'a has been inhabited for more than 2,500 years and has been a UNESCO World Heritage Site since 1986. The culture has been preserved in more than 100 mosques and 6,000 houses that were constructed before the 11th century.

Due to the dangerous conditions in the country, it's incredibly difficult for USA folk to visit Sana'a. The government has suspended the issuance of visas and there are very few hotels around the city willing to accommodate US visitors.

17 Havana, Cuba - Old-Fashioned Charms

Founded by the Spanish in 1519, Havana was a critical port throughout the 17th century and well known for ship-building. Today, it's home to over 2 million people and is well-known for its unique culture and style. The colorful, Spanish-influenced buildings, classic cars, and beautiful waterfronts are amongst the many popular attractions for visitors to experience.

But for US citizens, it's not easy to visit the vibrant city. While you can visit Cuba, you need to travel with a licensed tour group. You also have to stay at hotels that are civilian-owned or make a brief visit as part of a US cruise itinerary.

16 Boali, Central African Republic - Waterfalls and Exotic Wildlife

Located 100km northwest of the nation's capital, Boali isn't the largest city in the Central African Republic, but it is home to some of the most beautiful places. The massive waterfalls are a popular place to visit. While TripAdvisor reminds potential visitors that the falls only flow during the wet season, those that have been there made it clear that it's well worth a trip to experience the falls and the beautiful scenery around town.

The recent conflict in the country has made travel to the area nearly impossible for US visitors. The U.S. Department of State has issued a travel advisory for civilians because of the unsafe conditions.

15 Yaren, Nauru - Big Things in Small Places

Nauru is a tiny nation in the middle of the Pacific Ocean. As the smallest island nation in the world, it isn't home to many popular tourist attractions, but there is plenty of natural beauty to be found. Yaren is home to stunning beaches as well as the Moqua Well, an underground lake, and the Moqua Caves.

USA folk that want to visit Nauru have to go through a strict screening process. Submitting their criminal records as well as a certificate of medical fitness are just a few prerequisites. Even with a thoroughly completed application, there's no guarantee that access will be allowed.

14 Luanda, Angola - Vibrant Culture and Seaside Views

The capital city of Angola is home to one of the world's most beautiful seafront promenades which runs along the Luanda Bay. Alongside a booming modern city, the 16th-century Fortress of São Miguel gives visitors a look into the country's history. The seaside is a vibrant cultural center, full of live music venues and innovative restaurants.

Travel to the city can be difficult because the Angolan government requires all visa applicants to pay their application fee, their invitation fee, their flight, and their hotel fee before they even know if they get the visa. Because of their past relationship with the USA, travelers almost never get approved.

13 Meroe, Sudan - An Archaeological Paradise

Meroe is home to some of the most stunning and well-preserved ancient architecture in the world, making it a dream destination for archeologists and history buffs from around the world. UNESCO describes the heritage site as, "the seat of the rulers who occupied Egypt for close to a century and features, among other vestiges, pyramids, temples and domestic buildings."

Travel to the country has been nearly impossible for USA folk since the 1960s. Sudan controls the number of tourists, the locations they can visit, and even what photos they can take, making it extremely difficult for eager visitors to get a good look at the historical structures.

12 Massawa, Eritrea - A Seaside City with Colorful History

Located on the Red Sea, Massawa is a busy port city with a colorful history. Britannica cites the mix of Italian, Egyptian and Ottoman influences for the unique architecture and local cuisine. Visitors often make stops at the old Imperial Palace as well as St. Mariam Cathedral to learn more about the local history.

But Eritrea is incredibly strict about who it lets in. While anyone can apply to visit the coastal country, the process to apply takes around 8 weeks. Even if the application meets all the standard requirements, there is no guarantee that you’ll be approved.

11 Paro, Bhutan - Mountains and Valleys

Paro is well known for its many historical and sacred sites in the valley region. Hikers and adventurers often place the area at the top of their bucket list because of the many scenic mountains and winding cliffside trails. The cliffside Tiger's Nest monastery is also a popular destination amongst tourists for its incredible views and storied caves.

Travel to Bhutan is incredibly strict and it’s impossible to simply book a trip on your own. Anyone interested in visiting this part of the Himalayas needs to hire a travel guide and pay for the entire trip upfront. Depending on the season, tourists are also required to spend about $200 - $300 every day.

10 Riyadh, Saudi Arabia - Modern Marvels and Ancient Wonders

Riyadh is the capital of Saudi Arabia and home to many modern marvels. Tripadvisor cites the Kingdom Centre with its massive skybridge as well as the Al Faisaliah Centre as some of the most impressive buildings to visit. The Masmak Fortress in the historical district offers visitors a look into the areas past.

The United States has restricted travel to many areas throughout the country that are particularly dangerous for American citizens. Tourists that wish to visit the city also need to be sponsored by a legal resident or citizen of Saudi Arabia.

9 Tehran, Iran - Beautiful Buildings Rich with History

Tehran is the capital city of Iran and home to some of the most beautiful buildings in the Middle East. Ornate mosques that date back centuries are a favorite amongst visitors. The Golestan Palace, which dates back to the Qajar dynasty features colorful rooms are complex stained-glass windows. There's even a museum dedicated to the ancient jewelry of rulers from the past.

But the lack of a US Embassy in the country has made travel difficult and dangerous for Americans who wish to visit the area. While it's still totally legal for USA folk to travel to the country, the Department of State warns against it.

8 Bujumbura, Burundi - Lush Landscapes and Waterfronts

Anyone who visits Bujumbura will be treated to some of the most picturesque views Africa has to offer. Long mountain ranges overlooking lush valleys combined with the ocean views from the port make this city truly beautiful. Kibira National Park is a favorite for anyone seeking exotic wildlife like hippos and birds.

But instability has made the country a dangerous place for tourists. The Department of State has strongly advised against travel for USA folk. Those who do venture there will have a difficult time finding accommodations within the city.

7 Erbil, Iraq - Living History

Erbil is the capital of Iraqi Kurdistan and holds some of the most beautiful and historically significant places in the region. As one of the oldest continuously inhabited areas in the world, there are centuries worth of history to uncover throughout the historic city center. Popular places include Citadel of Erbil, which offers visitors a glimpse into the past.

Conflict in the area has made travel to the city incredibly difficult. Plus, it’s nearly impossible for the US embassy to provide any services to USA folk traveling in the country, making it a risky place to go.

6 Fada, Chad - A Desert Unlike Any Other

Fada is the capital of the Ennedi-Ouest Region of Chad and is home to ancient cave paintings as well as unique rock formations. The Telegraph cites, "the vast desert dunes, a shape-shifting lake studded with giant monoliths, and the vast Tibesti mountain range," as some of the most beautiful geological wonders.

But the country has been off-limits to regular tourist visits for some time. The US Embassy can't provide services outside of the capital city, making it dangerous for US visitors. Those who do wish to visit also need an official invitation letter from a citizen or a hotel.

5 Local: Club 33, Disney World - The Most Magical Place You'll Never See

Disney World is a popular destination for families and thrill seekers alike. Thousands of people visit the park every day to experience the thrilling rides and visit with their favorite Disney characters. But there's one place in the park that very few visitors ever get to see the inside of.

Club 33 is an exclusive, members-only retreat away from the hustle and bustle of the busy park. Walt Disney himself used to use the space to entertain his high-profile guests. People who wish to join as a member have to pay a staggering $25,000 just to get on the waiting list. Once you're in, you have to follow a strict set of rules.

4 Local: The Coca-Cola Vault, Georgia - America's Best Kept Secret

It's not uncommon to hear about popular foods having a secret ingredient or recipe that sets it apart from the rest. Coca-Cola is one of the world's most popular brands and almost no one actually knows the secret formula for creating it. While guests can visit the HQ in Georgia and view the outside of the vault, they won't get any closer to learning the company secrets.

According to Coca-Cola, "the secret formula for Coca‑Cola represents over 125 years of history, special moments, memories and the timeless appeal associated with Coca‑Cola." It just might be the best-kept secret in the food industry.

3 Local: Fort Knox, Kentucky - Worth Its Weight in Gold

Fort Knox is home to a large portion of the United States gold reserve. The door of the vault alone weighs 22 tons and the interior is lined with granite walls. The public isn't allowed to know the exact value of what the vault contains as information isn't regularly released for security.

The vault is heavily guarded 24/7 and civilians aren't allowed anywhere near the valuable contents. Since its construction in 1918, it has been the home of the Declaration of Independence, the Constitution, and copies of the Magna Carta.

2 Local: Bohemian Grove, California - Secrets of Wealth and Power

Bohemian Grove is a massive, 2,700-acre campground in Monte Rio, California. The campground is privately operated and every year in mid-July it's transformed into a retreat for some of the most powerful men in the world. For most of the year, members are allowed to invite guests, but no one outside of a very small circle knows exactly what goes on there in July.

Famous members of the camp include Henry Kissinger, Tennessee Ernie Ford, Newt Gingrich, Herbert Hoover, and Richard Nixon along with other politicians and artists.

1 Local: Granite Mountain Records Vault, Utah

Just outside of Salt Lake City is the world's largest collection of genealogical records. The vault itself is carved deep into the side of a solid rock mountain and is guarded by a massive 14-ton door. It contains roughly 2.4 million genealogical microfilm rolls which are equal to nearly 3 billion pages of recorded information.

Little is known about how the church acquired these records which further perpetuates the mystery of the location. Because it's so secretive, there are many rumors and stories about other activities that the vault may be used for.

Sources: The Telegraph, Travel Channel, Vanity Fair, UNESCO