The site of the signing of the Declaration of Independence. Enough said. Experience it.
The Liberty Bell is a truly beautiful artifact from the very beginnings of the United States of America. The address given above is for the Liberty Bell Center, but the Liberty Bell itself is actually on Chestnut Street. I used to live a few blocks from the Liberty Bell, which is a cool area of Philly to live in. Many times at night I would walk on the north side of Chestnut between 5th and 6th Streets...and there it is in the window. You can actually get quite close to it. There is a big window facing Chestnut, but if you go along the east side of the building, there is a smaller window that gives you an even closer view. You can go by there any time, day or night, and it is a very deep and humbling experience to be in the presence of such history.
A relatively new museum, the Museum of the American Revolution is a must-see for anyone with interest in the American Revolution.
As stated on its website, "The National Constitution Center in Philadelphia brings together people of all ages and perspectives, across America and around the world, to learn about, debate, and celebrate the greatest vision of human freedom in history, the U.S. Constitution." If you are a history buff, it is a great place to visit while in Philadelphia.
One of William Penn's original public squares in Philadelphia, Washington Square is not as famous or glamorous as RIttenhouse Square. Nevertheless, it is more significant from a historical perspective. In the past it was a burial ground, including serving as a military cemetery for American and British soldiers during the Revolutionary War. The Tomb of the Unknown Soldier of the American Revolution is in Washington Square Park. It is a very moving monument with an eternal flame in front of a statue of George Washington behind which is a wall with the powerful inscription: "Freedom is a light for which many men have died in darkness."
They are moving words in a beautiful park made even more poignant by the knowledge that, as you walk through the park, you are walking also walking through a historical burial site where the bodies of those who fought in the war that created the United States of America find their eternal rest.