Amy C.
Yelp
I've been going to the Seashore Trolley Museum since I was probably around 10 years old and it remains, to this day at 27, one of my favorite places to spend a day when I'm back home in New England. The entrance fee is nominal, and your money goes to maintaining the operations of the museum as well as the restoration of the various vehicles the museum has on display, so it's money well spent.
Seashore is great whether you're a kid or an adult. For the price of admission, you have access to a huge collection of trains, trolleys, buses, and other public service vehicles, in addition to unlimited trolley rides down a mile or so of track that traces the route of a former rail line, while the conductor gives you a history lesson on the museum and the rail route you're riding. There's also a restoration shop with an overhead catwalk, where you can look down and see various trolleys being repaired and restored. When you've finished your stay, hit up the gift shop for some fun toys, souvenirs, books, or t-shirts.
Some tips: you're going to be doing a lot of walking, so wear comfortable shoes! I'd recommend steering away from sandals as some of the ground is sand and gravel. Also, since a lot of the museum is outdoors, sunscreen is a good idea, or a sun hat or parasol if you're susceptible to sunburns or don't do well in the heat. Also, there are no food facilities on site, so either plan to grab lunch before or after your visit, or bring a picnic lunch to eat there.