Once Beethoven had reached the summit of the Ninth, he turned away from the outside world. This talk explores the radical shift towards his late String Quartets (from No. 12 to No. 16, including the Grosse Fuge). The laboratory is no longer concerned with proclamation or with building “monuments”, yet it never truly closes. In these final experiments of the Beethoven Laboratory, some heard “horrors” (Spohr); others, the purest and most timeless “contemporaneity” (Stravinsky); some, the deepest “melancholy” (Wagner); and others, an “impossibility” (what is left to write?, Schubert is said to have asked). One kindly critic seems to have written: “We know there is something there, but we do not know what it is.” Let us find out.