Fort Sumter National Park is based, on the mainland, at Liberty Square. There is a quite nice, if small, exhibition hall giving context to Fort Sumter and it's meaning. This hall is free. If you'd like to visit Fort Sumter itself, the price is quite hefty. The Park service has a contract with Spiritline cruises to provide transportation to and from the park. You pay ~$13 to ride back and forth from the island on the Park Service boat. There is a recorded narration that plays on the way to and from, but it basically gets drowned out by people (schoolchildren especially) running around and talking. The ride is quite cold, even if the weather seems nice for the day. When you arrive at the fort, you're given one hour before the boat departs to go back to the mainland, which is in no way enough time to listen to a Park Service guide give an overview of the place, go through and read the exhibits in the museum, and observe the ruins and explanations that are posted near them. My roommate and I (prolific readers) perhaps only got 40% through the fort in the time we were allotted. Quite a disappointment.