Guarapari, Brazil

With a population of just 61,719, Guarapari may seem like a sleepy coastal town, but its reputation as a popular tourist destination comes with some significant drawbacks. The city's beaches are famous for their high natural radioactivity levels, with some spots registering up to 55 μSv/h - over 150 times the average exposure in the United States. While the radiation levels are lower in the city itself, averaging 0.6 μSv/h, this persistent bureaucratic headache is a constant concern for residents. Additionally, the town's dramatic seasonal population fluctuations cater heavily to tourists, leading to an overburdened infrastructure and services. Guarapari may offer sun and sand, but those seeking a quiet, low-key coastal life would be better off looking elsewhere.