I went to the Grand opening and there was no need to make a reservation... I'd give them a call if you were considering taking a large group otherwise I don't think a reservation is required.
My husband and I went on a whim and were able to talk with a park ranger at the visitor center for a bit. They have a great map of the area highlighting the underground railroad stops. We drove around to a few. But I agree with A Duncan, you could always call the park service.
I would contact the Maryland Park services for more information.
How much time would you recommend for visiting Harriet Tubman Underground Railroad National Historical Park with its visitor center exhibits?
Reservation is not needed
If you are taking a group go to the website. There is a form for groups.
The Harriet Tubman Museum was free when I was their in June 2017 and it has walking tour inside the Museum with a gift store.
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