My husband and I have lived part-time in Mexico for 20 years. I walk all the time when I'm there and am now fluent in Spanish. The author and her husband live about half the year in Guanajuato, Mexico. Courtesy of Louisa Rogers My husband and I bought our house in Guanajuato, Mexico, 20 years ago. We spend about half the year there. I walk all the time when I'm there and have become fluent in Spanish. A few weeks ago, my husband went on a three-hour hike to a hill called Cruz Azul, above Guanajuato, the Mexican city where we live about half the year. When we left, we simply locked our door and started walking. We love that without getting into a car or a bus, we can be hiking in 20 minutes — one of many health benefits of living in Guanajuato. Living here is great for my physical health Because our home is so central, we come and go frequently throughout the day. We don't have a car, and don't want one.…