“The Capitol Visitor Center welcomes visitors from across the United States and around the world.
Identification is not required to enter the Capitol or to enjoy a tour.
All tours, programs and activities are free of charge. “
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Source : "How Do I Tour the U.S. Capitol and See Congress in Session?"
https://washington.org/dc-faqs-for-visitors/how-can-i-tour-capitol-how-can-i-see-congress
"A public tour of the U.S. Capitol is free and open to anyone who makes an advanced reservation, although there are some same-day tickets available
by standing in line at the U.S. Capitol Visitors Center (note that lines will be long during spring and summer).
This has always been my understanding too. While there may be restricted areas in the building, the biulding it’s self is public access.