Will be heading from Europe to Australia and have several options for stops. Some have 10hour+ layovers, so I am wondering about utilizing them. Is there a "minimum" time needed to attempt to leave an airport and "meander" between flights? Or is it more dependent on the country/city?
It depends on the city, airport, and access to transportation. I have done this at Copenhagen, where there is a train stop at the airport, and direct connection to the downtown station. I would recommend this for very congested cities, you might find yourself in a huge traffic snarl, if say, you use a cab, and you start fretting how to get back to the airport, takes all the fun out of it. Unless you are traveling very light, you'll be lugging stuff around, about 6 years ago