Address: 1000 Robert E Lee Blvd, Stone Mountain, GA 30083
Admission: $15 parking fee per car. Free if you don't arrive by car.*
Acres: 3,200
Approximate miles of trails: 15
Hours: Hours vary. You can check the hours here.
Miles from downtown Atlanta: 15
MARTA directions: You can take the 121 bus from Kensington station to downtown Stone Mountain (corner of W Mountain St and Main St). From there, walk South on Main St. In a few blocks, you will see the PATH trail on your left. The trail will take you directly into the park. It's about a 10 minute walk from the bus stop into the park, although the walk might be much farther to your destination within the park.
Cycling directions: The Stone Mountain PATH trail connects Stone Mountain Park to downtown Decatur, downtown Atlanta, and the BeltLine

* There is some free parking available downtown in the town of Stone Mountain, GA. From there, you can bike or walk the Stone Mountain Trail into the park without needing to pay an entrance fee. There is another pedestrian entrance on E Mountain St. Where the road turns left before entering the park, you can walk straight into the park instead of going left. However, this gate is only open from sunrise to sunset.

Links:
Stone Mountain Park
Maps