Depending a bit on the season you're traveling. If during the summer, even though you'll have "done" the beach in SC, you may want to stick to the coast for more beach time. You could consider the Chesapeake Bay Bridge/Tunnel https://www.cbbt.com/ a nifty 20ish miles long bridge (with a brief-ish length tunnel) at one of the outermost points of the ... Chesapeake Bay. I remember going over it with may parents years ago and me and my siblings being amazed. That could take you up towards Chincoteague - google it, big national park with native horses that have been written about for kids and adults. Those are my quick-ish, ideas.