then you need to take in the "Best free show in Charleston" and that is the weekly parade put on by the Citadel Cadets. It is held most Friday's when school is in session, around 3:45 (sometimes start at 4:20). The Corps of Cadets march on the parade field, accompanied by the Pipes and Drums. If you are lucky, the Summerall Guard will also perform. They are the silent drill team that represents The Citadel.
Other things that are very interesting if you like history are a visit to the Yorktown and a boat ride out to Fort Sumter. The ticket boothes for both are at the same location at Patriot's Point, just across the new bridge in Mount Pleasant. If you have the time, you can also ride out to Sullivan's Island and take in Fort Moultrie, which has an exellent view of Fort Sumter.
Other than those, if you just like tours, you can find one downtown that will take you to a lot of the historic places in the area, including many of the old churches that earned Charleston the title of the Holy City, and there is a very nice Aquarium on the waterfront downtown.
We will be at HHIR in March and April also. Hope you have a great time.