Traveling is fun, but it isn't always easy. Delayed flights, lost luggage, and awful weather are all things you'll end up contending with if you travel often. That's all assuming you can even get to the place you want to visit in the first place.

Some travelers are fueled by the desire to see everything, like 21-year-old Lexie Alford who just became the youngest person to visit every country in the world. If you count yourself among them, or if you're just interested in visiting far-flung places that few people will ever see, there are a few things you'll need to know.

Most importantly is the fact that some countries are tougher to visit than others. This can be for a few different reasons, from limited travel visas to restrictions on who can enter in the first place. There are a fair amount of difficult-to-visit countries, but you'll have the hardest time making your way to these five nations.

5. Iran

Political conflict and negative headlines in the press dissuade many from wanting to visit Iran, but beyond its political controversies, the country itself is home to some beautiful natural scenery, historic sites, and fascinating culture. Visiting isn't exactly easy, however. Not only do visa applications take much longer than many other countries, but there are travel restrictions for American, Canadian, and British citizens, while Israeli citizens are denied entry outright.

If you plan to visit Iran, make sure to start your paperwork long before you actually plan to arrive. You also don't want to visit the country on the same trip as a visit to Israel, as this will ensure you're denied access.

4. Turkmenistan

Turkmenistan is one of the world's stranger countries. The capital city Ashgabat is a white-marble oasis in the middle of barren desert, and while there aren't an abundance of tourist activities, there is a heap of fascinating history. Plus, it's worth visiting for a glimpse at the Karakum desert, where you'll find the "Gates of Hell", natural gas craters that look like, well, exactly what the name implies.

But you can't simply visit Turkmenistan as you would many other countries. You'll need to hire a travel company to help you gain access and escort you into the country. Even this step doesn't guarantee that you'll be able to make it in, as you'll need a letter of invitation to ensure you're allowed across the border. While hiring a travel company will give you greater odds of acquiring the letter of invitation, it doesn't guarantee entry. Roughly 20 to 30 percent of tourists who apply for the letter are denied.

3. North Korea

It shouldn't be surprising to find out that this secretive nation doesn't just let anyone in. Few wish to visit, and even fewer are allowed in to experience life in such an insular country. Visitors can only access North Korea as part of an organized tour, and even then restrictions on certain nationalities are always changing with the political tides.

2. Nauru

Nauru is not only the world's smallest independent republic, but it's also the world's least-visited country. This remote and sparsely-populated island means it's particularly pristine, and visitors who do make the trek will enjoy tropical vegetation and turquoise lagoons with little to no crowds.

Nauru's remoteness is only part of the reason it's tough to visit. Foreign visitors need a visa in advance, and the country is quite strict about who it will let in. If you're from another Pacific country things are easier, and this is true for Russian and Israeli citizens as well.

Once your visa application has been accepted, you actually need to get there. There is only one flight a week from Brisbane, Australia as well as a few flights to and from surrounding islands. Basically, once you get there, plan on staying for a while.

1. Eritrea

Like many of the countries on this list, there's a reason Eritrea is difficult to visit. The government's human rights record is among the worst in the world, and it comes in near the end of the World Press Freedom index. Unless you're from Kenya or Uganda, you'll need an entry visa to get in. There's no guarantee you'll actually receive one, and many people have had to apply multiple times before actually succeeding in entering the country.