Mongolia's largest lake by volume is Khovsgol Lake, a crystal-clear freshwater lake the size of Rhode Island located just a few miles from the Russian border. It's popular with holidaymakers from both sides of the border, and increasingly with adventurers from overseas as well. But I'm not here to sell you on the region's unspoiled pine forests, horseback riding, wildflowers and reindeer. For me, Khovsgol Lake is all about one thing: the world's smallest navy.

Khovsgol Lake is as pristine as Lake Baikal.

Lake Khovsgol probably formed about the same time as its more glamorous sister lake, Baikal, two or three million years ago. This makes it one of the dozen or so oldest lakes on the planet, and the millennia have left it essentially untouched ecologically. It holds 70 percent of Mongolia's freshwater, and on a clear day visitors can see as far as 140 feet down to the lake bed.

Mongolia is a landlocked steppe the size of Western Europe.

Eight hundred years ago, the Mongols, led by Kubla Khan, had the world's largest navy. But in the 13th century they lost their ships to two giant typhoons when they tried to invade Japan. (The Japanese called these fortuitous storms "divine winds," or kamikaze, which is how that word entered their military lexicon.) And then they lost their seacoast altogether. Today, Mongolia is the largest landlocked nation in the world—apart from Kazakhstan, if you don't count the Caspian Sea. Mongolia's only international water border is three square miles of Uvs Lake that crosses into Russian territory, so they don't really need a navy anymore, right?

Khovsgol is home to what's left of Kubla Khan's fleet.

In fact, Mongolia does still have a navy: a single tugboat with a crew of seven that patrols Khovsgol Lake. Keep in mind that Khovsgol Lake is surrounded entirely by Mongolian territory—a lovely national park, in fact—and you'll understand that the gallant crew of the Sukhbaatar III doesn't see a lot of combat duty.

In the Mongolian navy, you can sail the zero seas.

According to All at Sea, a 2001 documentary about Mongolia's one-tugboat navy, budget cuts have essentially privatized the Sukhbaatar, which now has to spend its off-duty hours hauling freight and tourists around Khovsgol Lake. But maybe it's a good thing that the Mongolian navy won't be sailing into battle anytime soon. As of 2001, only one of the country's seven sailors knew how to swim.

Explore the world's oddities every week with Ken Jennings, and check out his book Maphead for more geography trivia.