My husband and I will have a 22 hour layover in Vienna next year. We are Americans. What documents do we need to leave the airport to explore the city during our layover? Do we need a visa or something else to lawfully leave the airport? We will be traveling from Athens back to the US. We plan to stay at an airport hotel overnight.
Greece and Austria are both members of the Schengen agreement. So, there are usually no checks when travelling between these countries. Rather like travelling between states back home. Even if you are checked for some reason, your US passport will be sufficient; you may stay in the Schengen area for tourism for up to 90 days (out of 180).