The visitor does need to be careful in Guatamala City, which has some fairly dangerous neighborhoods. Though the country's civil war ended in the 90s, it left behind a large number of weapons and some people still eager to use them, which hasn't helped the city's crime rate. The "Zona Viva" area where most tourists stay is reasonably safe, but exercise care in the rest of the city, and don't venture into unfamiliar areas without guidance. Hiring a reputable driver doesn't cost that much and may be a good idea if you plan to spend a lot of time exploring.