"The Isenheim Altarpiece was executed for the hospital chapel of Saint Anthony's Monastery in Isenheim in Alsace [...] The work of Grünewald expresses the torment of the early sixteenth century more fully than that of any other artist. [...] [It] was painted before Luther nailed his theses to the door of Wittenberg Cathedral in 1517, but it is painted by a man who, like Bosch, used his great technical powers to express a simple, unmistakable message of emotional intensity and terrible realism." (source) - It might appear odd that I'd link to this, but somehow, I recently managed to stumble upon quite a few references to the altarpiece (for example in Michael Kimmelman's The Accidental Masterpiece
