Nea Smyrni, Greece

With a population of just 22,074, Nea Smyrni feels more like a crowded village than a modern Greek city. Refugees flooded in after the 1922 Burning of Smyrna, and the town has grown into one of the most densely populated places on Earth. Sure, the Alsos Neas Smyrnis park offers some green respite, but the stifling summer heat and persistent bureaucratic headaches are hard to escape. If you don't mind living elbow-to-elbow with your neighbors, Nea Smyrni could work - but for most, the lack of space and creature comforts would be a dealbreaker.