All tours of the White House are free. Public self-guided public tours permit visitors to move from room to room at their own pace; once inside the White House, most tours take about 15 to 20 minutes. Visitors usually walk along the ground-floor corridor and look through the doors of the Vermeil room and Library, walk upstairs to the State floor, and through the East, Green, Blue, Red, and State Dining rooms and exit from the north portico lobby. A U.S. Secret Service Tour Officer is stationed in each room to answer questions.