You can't climb on board the current Air Force One unless you're very lucky, but you can explore an older model if you wish. You'll find a retired Air Force One plane at the Ronald Reagan Presidential Library at Simi Valley, California.
Usually, when an Air Force One plane is retired, the plane is broken down and scrapped to protect the secrets of the technology onboard. That makes the public display unusual - but we suspect anything valuable or revealing has been carefully stripped away.