In October 2016 my friend Jeffrey and I took a coach from New York to Philadelphia for the day for the purpose of touring Independence Hall.
It costs nothing to go on the tours, which are conducted by official Park Rangers from the US Parks Service. Our guide, Larry, showed us the room where the Declaration of Independence was signed in 1776, as well as the former home of the US Senate and House of Representatives (they were based in Philadelphia after moving from New York but before Washington, D.C. was ready to receive them).
The concepts of freedom and democracy these men espoused (though they cared less about slavery) have since spread around much of the world and changed it largely for the better. The USA was the first democracy in modern times, standing in contrast to the monarchies that would still control most of the rest of the world decades or centuries later.
Later that week I travelled to the home of Jefferson in Virginia, which, like Independence Hall, features on US currency (the nickel and the $100 bill, respectively).