For a quick idea of whether you’d need a Visa to be allowed foreign entry into a specific airport, try layoverguide’s right hand widget.

To get more specific information on U.S. entry into foreign countries, check out The U.S. Department Of State Travel Site.

The website covers:

Location of the U.S. embassy or consulate in the subject country, unusual immigration practices, health conditions, minor political disturbances, unusual currency and entry regulations, crime and security information, and drug penalties.

There are many factors to take into account when deciding whether you have enough time to leave the airport during a layover and venture out into the surrounding area.

Before you leave, check with your airline to see if your ticket permits you to leave the transit area. Some tickets may not permit you to leave the airport. It is also helpful, if possible, when checking in for your flight to check your baggage through to your final destination. If you can’t, you can always ditch your bags at airport lockers, Left Luggage offices, or even a cheap hotel room while you explore.

When determining your time frame, and whether you have time to leave the airport, here are a few things to keep in mind:

• Figure out how far the airport is from the area you’re looking to explore. Many airports are close to the city centers, while some aren’t. For example, the Narita Airport in Japan is quite a distance from Tokyo, while the airport in Amsterdam is about a 15 minute train ride. Always plan for delays, so budget extra time to and from for getting lost (if you’re not familiar with the destination), and if traveling by taxi, keep in mind traffic and rush hour.
• Check to see if, at the airport you’re having the layover, whether you’d have to clear customs to leave the airport and then go through it again to re-enter. The website to your particular airport can help you learn the procedures, as well as calling your airline.
• If you need to store luggage, keep in mind the time to both drop it off and pick it up.
• If you need to transfer money to the local currency, budget time to do so.
• In addition to immigration and customs, budget time for security. At some airports these lines can get lengthy. Layoverguide suggests arriving back at the airport two hours before your flight.

For additional layover tips, check out Can I Leave The Airport During A Layover, Catching Connecting Flights: What You Need To Know and “Tips For Making The Most Out Of Your Layover.”