Recommendations for things to do in Atlanta in October?

I just signed up to go to a medical conference in Atlanta at the beginning of October and am planning to stay a couple extra days afterward and explore the city, since the conference happens to fall during my week off. Does anyone familiar with that area have suggestions for things to do/see in town? I noticed there is a company that does bike tours like the one I did in Boston last year, but it looks like they don't offer them on the days I will have open (darn!). I would also be interested to know how the public transportation is and whether it would be reasonable/safe for someone not familiar with the city to rent a bike and use that to get around town (IOW, how are the roads/drivers? I do have a fair amount of urban cycling experience but it has been in cities I know pretty well)...would just as soon not have to deal with renting a car. The hotel where the conference is being held is right downtown. Any info is appreciated!