Just up the road a bit from Plymouth Rock is the Mayflower II, which is by all accounts an accurate replica of the original ship of Pilgrim fame. I couldn’t find any information anywhere on whether or not the ship’s to scale, but it’s likely nobody’s really sure what the original Mayflower’s measurements were.
…anyway, essentially you’re paying to walk around on a boat. Other than the inevitable “I’m on a boat” joke, unless you like history, you probably won’t care. But if you don’t like history, what are you doing in Plymouth anyway?
There’s the standard “props to show you what life was like back then” deal aboard the boat. Obviously, it’s all replicas.
After roaming the boat for a bit, you’re greeted by a small, partially hands-on museum. Some of the stuff’s pretty cool; check it out. Might as well; you paid to get in here, you know?