The birthplace of the nation, Independence Hall has been restored to its appearance at the time the Declaration of Independence and the U.S. Constitution was written. Guided tours are available.
If you go:
Tour reservations for Independence Hall are required except in January and February. Open every day except Christmas. Admission is free to both Independence Hall and The Liberty Bell.
Links:

143 South Third Street
Philadelphia, Pennsylvania 19106 USA
Phone Numbers:
Park Headquarters
+1 (215) 597-8787
+1 (215) 597-8787
Visitor Information
+1 (215) 965-2305
+1 (215) 965-2305