It's awesome to visit the huge USS Yorktown at Patroits Point in Charlestown. Here you can enjoy bright beautiful views of Charleston Harbor, its blue water and green marsh grasses. See the Arthur Ravenel Jr. Bridge in all its modern glory- you drive over it to get to Patriots Point, and also have fantastic views of it from the parking lot and the top of the USS Yorktown. Watch helicopter and boat tours go by. From here you can catch a boat to Fort Sumter on a two hour excursion.

You walk a pretty bridge to get to the USS Yorktown- come on a sunny day to enjoy the gorgeous views. Once there, you can watch a movie in the theater. A self-guided tour (yellow arrows) leads you around the USS Yorktown. On the top level, check out the fighter planes. This ship is really well cared for so you feel at ease walking around it and climbing its ladders.
At the end of your visit, don't forget to check out The Vietnam Experience, a fascinating area of Patriots Point that is included with your ticket. Here, it looks like you're in Vietnam. There is a camouflaged patrol boat, jeep ambulance, UH-1H Iriquois helicopter, and tunnel. The experience is auditory as well- you can hear the sounds of fighting like the soldiers would have heard in Vietnam. There are shacks to enter where you can watch videos about the war.
On this same side of Charleston, check out Mt. Pleasant Pier, where you can hang out under the Arthur Ravenel Jr. Bridge on swinging porch chairs. There is an amazing playground that looks like the bridge, and is in the shade of the bridge, perfect on hot summer days, too cold and windy on winter days. Here people play frisbee on the huge lawn. You can pick up a picnic at nearby Whole Foods or Trader Joe's to have on the lawn.
Or nearby, eat at Saltwater Cowboys, which has perfect views over the water. It is a true delight! Go to the top for panoramic views at sunset, or to the bottom level for a bar with cute lights and a fire pit. Or stay on the second level for wonderful views out their sweet windows. The food is just ok.
Continue toward the coast to visit Sullivan's Island, and either Sullivan's Island Beach (which is more exposed) or Isle of Palms Beach, which has a cute main strip, Ocean Blvd, where you can get a Ben and Jerry's Ice Cream in an adorable tiny red-roofed building. Between Sullivan's Island Beach and Isle of Palms, stop at Thompson Park to see the picturesque views of Breach Inlet and read the interesting history plaques. Also on Sullivan's Island is Fort Moultrie, a fascinating place to visit and easier to see than Fort Sumter.

Directions

USS Yorktown is located at Patriots Point in Charleston. The address is 40 Patriots Point Rd, Mt Pleasant, SC 29464. 
Open daily 9-6:30. Closed Dec 25. Closes early on July 4, Thanksgiving (fourth Thurs in Nov), Dec 24, and Dec 31.
Admission is $24 for adults, $19 for seniors and active duty military, $16 for children aged 6-11, free for children aged 5 and under and active duty military in uniform.

Click on map for interactive view