One of the best ways to discover the magic of Guatemala City is to do a visit to Downtown. Check the main plaza, the cathedral and also sign in for a tour of the National Palace of Culture (every hour during the afternoon). A few blocks away in the 7th avenue is The Post Office Building (Correos) where you can also find art exhibitions and dancers practicing. Cien Puertas is an area with several bars just behind El Portal in the main plaza and finally, don't forget to visit the Central Market behind the Cathedral. There you'll find three floors of basements. The first one is about food, fruits and restaurants. Recommended to visit Doña Mela for some tortillas with different recipes. And in the second basement you'll find all sorts of handcraft. In the third one amaze yourself with figures and materials to build your own ;)
Guatemala City is off the main attractions of the country, but it's worth a visit to the downtown.