Yes, you can technically leave the airport during an international layover, but it requires meeting three critical conditions: sufficient time, legal entry, and security re-clearance. First, you must have a "layover" of at least 8+ hours to account for deplaning, immigration, and the return security check. Second, you must have the legal right to enter the country; for example, a U.S. citizen in London or Paris can walk out freely, but a citizen requiring a visa for the Schengen Area would need a pre-approved Transit Visa to exit the terminal. Finally, you must clear Customs and Immigration to leave and Security/Passport Control to return. Note that in some countries (like the U.S.), you must clear immigration and collect your bags at your first point of entry anyway, making it easier to step outside if your connection is long enough.