Originally built to commemorate Atlanta's hosting of the 1996 Olympics, Centennial Olympic Park is still a wonderful place to visit in the morning, afternoon, or evening. The park is only a couple blocks west of two and north of one MARTA rail stations, thus, easily walkable.
Every so often there are free concerts, children's events, Screen on the Green (a free evening movie on the grassy lawn), and other events. In the winter there is also an ice skating rink.
One of the icons of the park, is the 5 ring fountain that is usually spouting water. For the locals, it's commonly used as a quick way to cool off during a hot summer day. Definitely worth a visit.
At night the fountain is lit up and all colorful.