For that length of time I would rent a car. There is a lot to do outside of the cities--the plantations, etc. Driving up the coast. I agree that Charleston is an imminently walkable city, but wait, there's more!!

With due deference to earlier posters, I would ask the following questions. Are you mainly interested in the history of the area? Are you iterested in the "modern" developments of the area? Is there a ethnic heritage of the area that is of particularly interest you? Are you a fan of architecture or are you a fan of nature?

I ask because, if you have a particular area of interest, the recommendations you receive may vary widely.

I confess, I am splitting hairs, because it all very, very, good!