The Library of Congress is a jewel box of tile work, not to mention the collections. Let me just amaze readers with numbers, taken from Wikipedia:
23,892,068 catalogued books in the Library of Congress Classification system;
5,711 incunabula (books printed before 1500);
14,067,260 monographs and serials, music, bound newspapers, pamphlets, technical reports, and other printed material;
and 122,810,430 items in the nonclassified (special) collections:
160,775,469 total Items
I had thought that I would find it but was still quite moved to learn that a copy of my grandmother Dorothy Leonard's small self-published book of poetry, Buttressed from Moonlight, is here and entered in the digital catalog.