If you're planning a trip anywhere in Europe, it pays to look at Turkish Airlines' fares, since they often beat other airlines by hundreds of dollars. The catch is that you'll connect in Istanbul, and your layover might be eight hours or more, or even overnight. But is that so bad? Not if you like two-for-one deals. Not only do you get Rome or Paris, but you also get a free tour of Istanbul. And a free lunch.  

Several airports, tourist boards or airlines, in order to promote tourism, offer free airport layover tours.  

Istanbul

Turkish offers three tours from Ataturk Airport, showing visitors Istanbul's highlights. You get picked up and dropped off from the terminals. Tour 1 runs from 9 a.m. to 3 p.m.; tour 2 from 12 p.m. to 6 p.m.; and tour 3 from 9 a.m. to 6 p.m. For those who think there's no such thing as a free lunch, there is: lunch is included ("you're our guest," as the website makes clear more than once). If you prefer, you can also get a free overnight hotel stay, but no, you don't get both freebies.    

Seoul

The Korean Tourist Board offers free transit tours at Incheon International Airport. Choices include an Incheon City Tour, Seoul City Tour, Temple Tour, and several others, lasting between 1 and 5 hours. Although the tours are free, any site admission fees must be paid by travelers.  

Taipei

Free half-day tours are offered on a first-come basis, and are limited to 18 passengers. You can choose between morning and afternoon departures.  

Singapore

If you have at least a four-hour layover at Singapore, Changi Airport offers two free two-hour tours of the city-state.  

Other tourist boards and airports also suggest transit tours, but they're not necessarily free. The Hong Kong Tourist Board, for example, suggests two tours, one of Hong Kong Island and the other of Lantau island, for about $85 per person.

There's a similar tour offered at Bangkok's Suvarnabhumi Airport.