Most homes in Mexico don’t have central air. They keep the windows open with fans blowing during the day. In the evening, the temperatures drop outside, cooling the home inside.
Because windows are left open all day, you’ll find that they have bars across them for security. In Mexican towns, many of the people walk through the streets. The streets are narrow, so there aren’t as many cars per household as there are in the US. With this increased foot traffic, the metal bars keep families safe, but don’t have to look menacing, either. Most people decorate their window ledges with plants which draws attention away from the metal bars.