I agree that you should spend 3 nights in Charleston and the suggested activities are good.  However, I would go to Sullivan's Island (instead of Folly) and I would also avoid the market (very touristy).  Explore Upper King Design District, perhaps a plantation tour, or even a tour of the Charleston Tea Plantation.  After three days, head out in the morning to to Columbia (I-26 to I-77 towards Charlotte) and then Exit 5 to the Congaree National Park.  Spend the morning there.  Eat lunch at Motor Supply Company Bistro on Gervais Street and then spend the afternoon on the Riverwalk, or at the South Carolina State Museum, the Columbia Museum of Art, or the Woodrow Wilson Family Home.  Spend the night at the Inn at USC Wyndham Garden.  After an early morning stroll through the University Hill neighborhood or the South Carolina State House (or alternatively the Riverbanks Zoo and Garden), take I-26 North to Greenville. Many things to do in Greenville for a couple of days, including a wonderful Main Street, the Swamp Rabbit Trail, and the Falls Park on the Reedy.  For your final day, Caesars Head State Park is a good outing.  When ready to go to Atlanta, it is just over a two hour drive.

Hello,

South Carolina and Georgia (State) has a lot to offer and while it is possible to keep busy for all six days in Charleston, I agree with you that you should try to make the most of your time in the region. I will just start by listing some things I think you would like in Charleston, and then some other destinations worth visiting that are also in reach. While the number of days you spend in Charleston really depends on your personality and travel style, I personally would probably spend 3 days there and 3 days split between the other places I will mention below.

Charleston:

• If you enjoy walking and want to learn more about the city, I would suggest taking a walking tour. Charleston has many great options to choose from including highly rated Charleston Footprints and Oyster Point Historic Tours.
• White Point Garden is a great place for a stroll as well with great views of the water and Charleston's historic homes.
  
• If you want more beach time after leaving Hilton Head Island, I would head to nearby Folly Beach.
• Saint Michael's Church is definitely worth stopping in and is included on many walking tours. It has a fascinating history and beautiful Tiffany stained glass.
  
• Try some local beers! You could do this by tour such as Original Pub Tour of Charleston which offers walking tours of historic downtown pubs or van tours of the areas microbreweries. 
• Historic Charleston City Market is a good place to hit up for local products, handicrafts, and artwork. 

Charleston Restuarants to try:

• 167 Raw: Try the ceviche, shrimp tacos, oysters, and lobster roll.
  
• Cru Cafe: Try the pressed pulled pork sandwich, smoked turkey and brie sandwhich, sweet tea, and local grilled swordfish.
  
• Five Loaves Cafe: Try the southern benedict (with green fried tomato and pimento cheese), sweet chili glazed eggplant wrap, and pumpkin seed encrusted salmon. (Brunch items on Sunday only)
• Circa 1886 Restaurant: Try the sea scallops, rabbit leg confit, and burgandy crest salad.
  

For more ideas on Charleston attractions and restaurant check out their Trip Advisor Page.

Other Destinations on route to Atlanta:

• Savannah: You would backtrack past HHI, but the historic area is just beautiful!
  
• Augusta: On route to Atlanta and has great sites including the Morris Museum of Art with a great southern art collection.
  
• Near Augusta is Phinizy Swamp Nature Park which has beautiful scenery and leisurely walking trails.
• The Georgia Museum of Art is located in Athens (Georgia) and is also on route to Atlanta.
• Greenville: This is a little bit out of the way, but a great choice if you would like to take in a more mountainous landscape including Falls Park on the Reedy.
  

And don't forget the many attractions in Atlanta. You could consider spending a day or two there as well.

I hope this was enough to get started! Feel free to contact me at The Travelers Toast if you would like some more personalized suggestions based on your travel style and budget. 

Happy Travels!

I assume you will be driving from Hilton Head IslandHilton Head to CharlestonCharleston. I would take one night and 2 days and enjoy either SavannahSavannah, Ga. or BeaufortBeaufort, SC "on the way". Savannah is a little out of your way but an easy trip between both HHI and Charleston. Stay in the historic district in Savannah and really play tourist: carriage rides, known restaurants, and the tours that teach you about the history both true and funky. Or, if you are going directly to Charleston, think about leaving early from HHI and spend one day in Beaufort, a lovely seaside town, decent food and just a pleasant 4 hours of walking and enjoying. HHI is about an hour to Beaufort and Beaufort another hour and a few minutes to Charleston. There is no "one Charleston". If you plan to spend the entire week, I would suggest for at least 2 nights and three days, go on tours. Head out to Middleton PlaceMiddleton Place for a breathtaking day on this historic plantation. Head to one of the beaches, any one. Personally, I am fond of Sullivan's IslandSullivans. Take a Ft. Sumter tour via boat. Visit the South Carolina AquariumSC Aquarium, pay to take a backstage tour... so worth it. Then eat your heart out. Hard to have a bad meal in this great city. Have fun!