Arlington National Cemetery is a military cemetery on the grounds of the home of Robert E. Lee near the Potomac River and near the Pentagon. There are tombs of many U.S. presidents, militarymen, celebrities and astronauts. It is open from 8:00 to 17:00 (until 19:00 from April to September), and entrance is free. Also In this lies the Tomb of the Unknowns where the Changing of the Guard ceremony takes place every hour in winter and every half hour from April to September. Without a doubt the most famous tomb for visitors to see is the tomb of the former President Kennedy.