Fort Sumter, now a national monument, is completely accessible with lifts taking you to its several levels. Unfortunately, the ferry that takes you there is not. A stairway must be negotiated to get onto the boat. Because they are a park service concessionaire, the crew are obligated to get you on nonetheless and they will cheerfully do so. The fort is on a small island in the bay and can easily be seen in the 90 minutes the ferry company allows you to explore.
Rangers are on hand to point out and interpret the various features and lore.
One bit of information was that the world's first submarine, used to sink a Union ship during the war, sits on the bottom of the bay not far from Fort Sumter. Charleston is served by major airlines such as US Air, Amtrak, and Greyhound. We flew into Charlotte, North Carolina, rented a van, and drove in. Accessible public transportation is very good here. The DASH shuttle bus system serves the historic core with fares ranging from free to 75 cents.