Open Mon.-Sat. 8:30-4:30 for walk-in visitors; Mon.-Sat. 8:30-5 (also Mon. and Wed.-Thurs. 5-9:30) for researchers. The building is occasionally closed to visitors during special events. Guided tours are given Mon.-Fri. on the half-hour 10:30-3:30, Sat. at 10, 10:30, 11:30, 1:30 and 2:30. Tunnel to the U.S. Capitol Visitor Center open Mon.-Sat. 8:30-4:20. Closed Jan. 1, Thanksgiving and Christmas.