I used to live on Cape Cod and *never* went to the beach in the summer! You should try at least one ride on the Cape Cod Rail Trail, although it'll probably be very busy in the summer. Check out the National Seashore. Lots of little hikes, and good history. Because the Pilgrims landed there first (before Plymouth), the Seashore has an interesting combination of natural history and people history (jump on the rail trail in Harwich and you can ride to the visitor center). I'd say there's more seafaring history than railroad history. The rail trail has informational kiosks every now and then, but I'm thinking you want it all in one place.

There is a scenic railroad leaving from Hyannis. I don't know much about it, though. I love visiting the Cape. I hope to go in May.