Agree that good walking about opportunities will be few. Marietta doesn’t really have a downtown so to speak. Various commercial areas should present themselves convenient if you’re staying in Marietta. One rule of thumb would be to not plan on being anywhere on foot after dark inside the perimeter (ITP). Interstate 285 that encircles Atlanta proper. The closer in to Atlanta you go the dicier (some very much so) the neighborhoods could potentially be. Not safe after dark for someone not familiar with the whole shebang. Cab services are available virtually anywhere if it’s in your budget. Not a terribly dangerous place but it is definitely life in the big city so be careful.