Spiritline offers a harbor cruise as well as operates the only ferry to Fort Sumter. The harbor cruise is narrated, usually hosted by a guide who draws attention to points of historical interest along the harbor.
It's one of the best ways to see Charleston. Spiritline also offers an evening dinner cruise.
This was the very first tours we took in Charleston and I think it was a good introduction to the Charleston Harbor.
When we went on the harbor cruise, the tour guide was a local man, who was really entertaining. His narration was very animated, telling stories all about the sites we encountered along the harbor.