Like anyone else, we love the idea of a free trip. And that's just what major airlines are offering when they advertise a "free" stopover in one of their home cities — essentially a bonus side trip to another city while en route to your final destination.

Not to be confused with a layover (a few hours in the airport while waiting for your connecting flight), a stopover is any stay longer than 24 hours in which travelers leave the airport and go explore the surrounding city. The length of a stopover is entirely up to the traveler, and since there is often no extra cost added to the original ticket, the stopover is considered free. (In airline speak, this is known as a "dual destination vacation.")

But how exactly does one go about booking a stopover? And is it a better deal in the long run?

First off, it is important to understand why certain airlines provide free stopovers. In almost every case, these are major international carriers based in major hubs (Emirates/Dubai; Singapore Airlines/Singapore; Japan Airlines/Tokyo; etc.) that want to lure more tourists to their destination. Enticing travelers with a "free" stopover leads to hotel bookings, restaurant meals, and other tourism dollars that otherwise wouldn't have been spent.

To book a stopover, select "multi-destination" or "multi-city" on the airline's website and plug in the specific dates for your desired stopover. As long as your stopover is in the airline's home city, chances are it will cost the same price as a ticket without a stopover.

For example, if I'm looking up flights from New York to Budapest in October, Kayak tells me that Aeroflot offers the cheapest route for $808, with a 3.5 hour layover in Moscow. If I then go to Aeroflot's website and type in a multi-destination trip that includes two days of sightseeing in Moscow, the flight is the exact same price: $808.

Here are some more examples: 

On Singapore Airlines, a flight from Sydney to London in October costs $1768, with a ten-hour layover in Singapore. However, if you try a multi-city itinerary that includes a three-day stopover (and who wouldn't want to do that?), the total comes to $1818 – just $50 more.

Hawaiian Airlines also allows passengers to stopover for free in Honolulu, their home city. A flight from New York to Tokyo, for example, costs exactly the same as a multi-city trip that allows for a three-day stopover in Honolulu.

When it comes to European destinations, Icelandair allows passengers to hang out in Reykjavik at no additional cost. And thanks to a partnership between KLM and Air France, folks can book a multi-destination ticket that yields not one but two free stopovers: Paris and Amsterdam. The "3 In 1" offer is valid for any European destinations serviced by both airlines.

Japan Airlines makes it super easy to make a stopover in their hub city, Tokyo. When searching for multi-destination trips, their website actually includes a helpful "stopover" button that allows you to build a stopover right into your trip. A New York to Bangkok flight in October ($1605) costs only $100 less than the same trip with a four-day stopover in Tokyo added on.

When dealing with multi-city itineraries, it's always worth playing around with different dates and departure times to find the cheapest options (this goes for both airline websites and third-party search sites like Kayak or Hipmunk). And if a website is yielding conflicting information, simply call the airline directly and ask. Yes, you'll be spending more effort than you normally would on a regular round-trip ticket, but, for the chance to knock out multiple destinations for the cost of one, the end absolutely justifies the means.