Update - Charleston SC - Looking for a few must-see ideas

If you go to Hominy Grill, do yourself a favor and get the chocolate pudding. It is the best ever - even Alton Brown thinks so.
You can go to Patriot's Point - from there you can go to Fort Sumter and there's a decommissioned aircraft carrier and submarine you can go through if you are into that sort of thing. You can go sailing out there as well - not at Patriot's Point but right next to it. There's a series of docks and signs.
Definitely go to Magnolia Plantation if you can.
There's several beaches obviously. There's dinner cruises you can take as well. Beautiful sunsets here right now!
King Street has amazing shopping and really pretty architecture.
You can take horse & carriage rides downtown to see the city. I love seeing the history down there, but it's hard to do in a car.

Skip the cooking class and just eat at FIG, Husk and the Rarebit (lunch). Please don't go to Hymans or Bubba Gumps for seafood, or Ruth Chris for steaks... Eat local!!!!
See a Riverdogs game
Isle of Palms is probably your best bet for a beach, or Sullivan's Islnd for a little more local crowd... While you're out there, eat at Poes for the best burger and Obstinate Daughter for seafoos.
Patriots Point, Fort Sumter and the Mount Pleasant Waterfront Park under the Ravenel Bridge if you're planning on renting a car... I'd recommend a car rental for at least one day for this reason alone, two days if you will go to the plantation
Magnolia Plantation or Middleton Plantation
Walk through the open air market for your souvenirs

Go to Husk, and I wouldn't wait to make dinner reservations here or any of the other suggestions. There are two Husk restaurants in the country, and one of them is here in Nashville. It's my favorite restaurant at the moment!

I also second the carriage ride. It's a great way to see the city and get some history. Try to do that early on in your visit. We also did a walking tour on another visit that was great, but I wouldn't recommend it during this time of year (hot, hot, hot).

Yeah, if you do the walking tour in the evening, that's not a bad idea. We did a ghost tour one either there or Savannah (I can't remember where exactly, I'd have to look through my scrapbook). It was fun, but later scared the bejezzus out of me and I couldn't sleep that night. Lol!

We did a ghost tour in Savannah and the tour stopped at the Inn where we were staying.  The tour guide said there was a little girl ghost that liked to pull on the covers while guests were sleeping.  Umm yeah, I had trouble sleeping that night!

Another vote for the carriage ride. I've also done tours of several of the historic homes down the the Battery (another good spot to walk around). They're really cool. I remember liking the Nathaniel Hawthorne house. If you rent a car another cool plantation is Middleton Place. The gardens are amazing. I thought Fort Sumter was a disappointment and I love history. The ferry ride was nice (you will likely need advance reservations), but the fort is in pretty bad shape.

Did you do a dolphin or sunset tour? If so you might be disappointed as there is no "tour", they literally just go around the harbor. The crew will answer questions but it isn't like on the larger tour vessels where they have spiel. We went on the dolphin one a month ago and LOVED it but we just wanted a harbor ride, we weren't looking for a tour. My daughter got to "steer" the boat and my husband helped hoist the sails. We will DEFINITELY do it again! I remember doing one of the other boats last year (one of the ones that have two levels) and that really was a tour. I can't remember what company it was though they all are kind of the same.

I like the carriage rides but my husband doesn't like the stinky mule butts so we didn't do one this time. Patriots Point is really cool but very hot this time of the year. So hot. We love Waterfront Park, my daughter loves the fountains and we love the swings or even just walking along under the tree canopy. Or even just walking along the roads near Battery Park and looking at the lovely houses. 

When we go we always eat at Hall's Chophouse and Cru Cafe. I always thought it was a tourist trap but my MIL and I had a surprisingly good lunch at Fleets Landing. We're not fancy/foodies so places like Husk and FIG never really appealed to us. 

If you plan to stay in the area, there are plenty of pedicabs but our last trip we found out about Scoop. Basically free rides, all you do is tip the driver. We usually tipped $10 and that came out cheaper than pedicabs and I felt safer in a car. We stayed at the Harbor View Inn and I think the longest we waited for one of the cars was 10 minutes and that was because we needed a larger car than they sent originally. We will use them again!

I agree with all of this.  Also, just walking around the battery is really nice.  

Charleston is one of my most favorite cities. So many wonderful places to eat. My favorite is Fleet Landing, right on the water. Have the crab cakes. to. die. for.

Downtown there is an extensive trolley system that goes all over the downtown area, and the visitors center is really nice, and will provide you with a wealth of maps/tickets to various tours etc. The Farmer's market on Saturdays in the square is really cool, and their downtown area is really nice and well developed with lots of places to shop and eat. If you want chain food, the Mellow Mushroom (which we don't have here) was very good and had a nice bar area. The city market is also really cool to walk through. If you go during the week- find the lemonaid guy. Their Arnold Palmer's are fantastic!

Be aware if you are renting a car that parking can be at a premium downtown. Many of the garages charge 15 bucks a day to park, and the hotel I stayed at in June charged 20.

Folly beach is within driving distance, and has a great pier area as well as a nice restaurant. The little store there sells ice cream along with t-shirts and fishing licenses.

Have fun!

Yes Hominy Grill is a must. Fleet Landing is great too. Make your reservations now for the restaurants that take them... You won't get in otherwise (particularly at Husk or FIG, both of which are not to be missed).