The library building is still in use today, and contains the famous Sistene Hall.
"This noble hall—probably the most splendid apartment ever assigned to library-purposes—spans the Cortile del Belvedere from east to west, and is entered at each ed from the galleries connecting the Belvedere with the Vatican palace. It is 184 fee long, and 57 feet wide, divided into two by six piers, on which rests simple quadripartite vaults. The north and south walls are each pierced with seven large windows. No books are visible. They are contained in plain wooden presses 7 feet high and 2 feet deep, set round the piers, and against the walls between the windows. . . .(Clark, The Care of Books  49-50).