We live in an always-on world, or at least that's the impression most of us have of it. Day after day, the media—which, to be fair, we access via said always-on devices—floods us with articles warning us of the danger of being too connected and also, simultaneously, the many benefits of disconnecting.
The locations on today's list will address both of these points. Indeed, there are plenty of places in the world that are not connected at all, some of which are much closer and more ordinary than you think. And, most importantly, very easy to access, which makes disconnecting by means of traveling to them a sure bet.
The American Desert
America is huge, and most of the country's land area is uninhabited. While certain countries (most notably China) have built cell towers at roughly equal distant from one another across their landmasses, the United States has failed to make such an investment. As a result, when you're driving in the desert southwest, there's a big chance you'll lose service, probably for hours at a time. Load your navigation before you leave the city!
It's probably not accurate to say cellphones don't work in North Korea. There's almost certainly a cellular communication network in place in the country, even if it's meant only for Kim Jong-Un and other government elite.
The problem with this, for everyone except Kim Jong-un, is two-fold. If you're an ordinary North Korean, you either (A) can't afford a cellphone or (B) can't buy a local SIM card (they don't exist) to put it in your cellphone and make it into anything other than a camera with a really crappy battery life.
If you're a foreigner, on the other hand, the nonexistent SIM card issue will affect you, but more than that, the government may choose to confiscate your cellphone upon entry into the country. You know, censorship and all.
In general, Japan is one of the most connected countries in the world, but there are a few caveats to this designation.
The first relates to where you are. Cellphones generally don't work in extremely mountainous areas, or onboard high-speed trains like the Shinkansen when they're traveling at full speed. (Curiously, they do tend to work on the metro and in elevators, but that's a discussion for another time!)
The second, which is mostly obsolete now thanks to loosening of rules in advance of Tokyo 2020, relates to the strange regulation of SIM card sale in Japan: If you're a foreign visitor (i.e. not living or working in Japan), it was very difficult to purchase a SIM card outright until very recently.
Cuba deserves some credit for the progress it's making with regard to telecommunication. Public Wi-Fi areas have opened up in cities like Havana, Trinidad and even remote Baracoa, making it easier for locals and tourists alike to get connected, even if lines to purchase vouchers can be excessively long and network speeds can be slow due to the popularity of hot spots.
Unfortunately, actual cell towers are still almost nonexistent in Cuba as of early 2016, and although recent action on behalf of the Obama administration will likely expedite the building of essential infrastructure in Cuba (provided that the Trump administration doesn't go back on this) it's going to be a long time before you can use your cellphone in Cuba, whether you roam with your U.S. carrier or buy a Cuban SIM—those aren't readily available at the moment, either, and probably won't be for some time.
Out at Sea or In the Air
It's no secret to most people that cellphones tend not to work in moving elevators or underground, such as in subway station. This is of course not a matter of physics, but it is nonetheless accepted as reality.
To be sure, while most people would also accept that phones don't work inside airplanes at cruise altitude, this is also due more to policy and lack of infrastructure, rather than availability or existence of technology. Dozens of companies around the world offer software and hardware to allow cell calls in-flight. In some countries (such as Brazil) this phenomenon is practically commonplace!
Out on the open sea is another place where you might not be able to use your cellphone. Granted, if you're on a large cruise ship, it might be equipped with satellite-based technology that allows you to connect to cellular networks with relative ease. But if you're on a smaller vessel—say, a yacht sailing through Myanmar's Mergui archipelago—you might find yourself marooned, technologically speaking.
(Then again, that might not be a bad thing, particularly if you're someplace extremely beautiful. Like, not North Korea.)