The Clock Tower sits at the north end of the Westminster Palace complex, immediately adjacent to the west approach to Westminster Bridge. The clock features the great bell known as Big Ben, together with four quarter bells, which play the Westminster Quarters on the quarter hours. (Click here to listen.) The clock is uncannily accurate, and is mic'd by BBC Radio 4 and the BBC World Service to serve to mark the top of the hour on their broadcasts. The twin spires of Westminster Abbey cast shadows on the House of Commons and the lower portion of the Clock Tower in the setting sunlight.