New global data released in June 2025 identifies key cities that represent the extremes of urban life—offering the cleanest air, preserving the oldest defensive walls, or ranking among the most dangerous places on Earth. In terms of air quality, the American Lung Association’s “State of the Air 2025” report found that several U.S. cities, including Honolulu and Casper, Wyoming, scored an “A” for year-round particulate pollution levels. Other top-performing U.S. cities with clean air include Bozeman, Montana; Bangor, Maine; and Kahului–Wailuku on the island of Maui. Globally, IQAir’s latest data highlights Auckland, New Zealand, and Dublin, Ireland, as among the cleanest cities for fine particulate air pollution, with annual PM2.5 averages well below WHO guideline levels.
As for historical infrastructure, archeological records confirm that the oldest standing city walls are located in Jericho, in the West Bank. Dating back to approximately 8000 BCE, the Neolithic walls of Jericho are considered the earliest known man-made defensive structures. In Europe, Chester in England holds the record for the longest complete city walls still standing in the UK, originally constructed by the Romans around 70 CE. Other notable preserved walls include those surrounding Nuremberg in Germany, Nicosia in Cyprus, and the medieval remnants in Edinburgh, Scotland. Spain’s city of Lugo in Galicia is recognized by UNESCO for maintaining its complete Roman wall circuit, constructed in the 3rd century and still encircling the old city center.
While some cities represent environmental or historical achievement, others rank high for public safety concerns. Crime statistics from various global tracking sources list Pietermaritzburg in South Africa, Caracas in Venezuela, and Port Moresby in Papua New Guinea as among the most dangerous cities in 2025, each with crime index scores exceeding 80 out of 100. The U.S. city of Memphis, Tennessee, also appears in the global top five, with a high violent crime rate, including assaults and homicides. Other cities frequently cited for elevated danger levels include Tijuana and Acapulco in Mexico, San Pedro Sula in Honduras, and Johannesburg and Durban in South Africa.
Together, these rankings offer a wide-angle view of modern urban extremes, from cities breathing the cleanest air or walking through millennia-old streets, to locations where personal safety remains an ongoing concern. For American travelers and policy observers alike, these lists highlight both inspiring global benchmarks and critical security realities.
