They are nowhere near as pretty in winter, but the plantation tours are pretty cool. Each is unique so perhaps look them up and see which one looks the most interesting (probably Middleton in winter).

I'm not sure if Cypress Gardens lets you take the row boats out in winter, certainly it isn't nearly as stunning, but paddling through the cypress swamp is pretty cool.

Golfing? Kiawah has the Ocean Course and several others. On the way out there take a stop at Angel Oak, the biggest oak tree you'll ever see.

A Ghost Tour is always fun. The carriage tours are fun, but incredibly over priced. I've always enjoyed parking at the Battery (White Point Gardens), strolling through the park and then down the city streets. So many private beautiful gardens that are hard to see if you're not walking on the sidewalks.

Savannah is a less crowded Charleston-lite. They do have the pretty town squares of Forest Gump bus stop fame. A bit of a drive from Charleston, though.

Mepkin Abbey is a hidden gem. Absolutely stunning views of the upper Cooper River. The grounds are open to the public, just be respectful and peaceful while out there.