Here's how to get a ridiculously cheap flight if you don't care where

Sometimes, when you are planning a vacation, where to go isn't the most important part of the equation.

For me, any number of factors can determine the destination: Is it relaxing? Is it interesting? Is it exotic? Have I been there before? If a destination hits any of those factors, I could be interested - as long as airfare is the right price.

While planning a recent vacation with no concrete destination in mind, I hit upon one of the best secrets in travel.

For those in the know, SkyScanner is one of the best travel booking sites on the planet. It searches through hundreds of different booking and airline sites to find you the best deals, but somehow it always seems to find cheaper international flights than other travel sites like Expedia or Kayak. In addition it has great features like airfare graphs to let you know whether you should buy now or wait for prices to drop.

SkyScanner's best secret, however, is for people who aren't too picky about the destination: It lets you search for flights all over the world to find the cheapest destination to fly into.

To search for flights all over the world, simply go to the SkyScanner flight search page and enter the city you are flying out of in the "From" box and then type in "Everywhere" in the "To" box.

Just in the quick search above, I found sub-$400 airfare to hot travel destinations like Puerto Rico, Virgin Islands, Mexico, and St. Maarten. Cheap U.S. flights on those dates include Florida (Orlando, Tampa, Ft. Lauderdale), Chicago, and Texas. If your dates are flexible, try out a few different searches.

There are also great last-minute deals. In August, I found a $350 round-trip ticket to Stockholm, Sweden, for just two weeks later. It's usually impossible to fly round-trip to Europe for anything less than $800.