A Black Mass is a ceremony celebrated by various Satanic groups. It has allegedly existed for centuries in different forms, and the modern form is intentionally a sacrilegious and blasphemous parody of a Catholic Mass.
The Guibourg Mass by Henry de Malvost, from the book Le Satanisme et la magie by Jules Bois, Paris, 1903
Sixteenth century woodcut depicting Black Mass
Engraving from a 1797 edition of Justine, by the Marquis de Sade
Là-Bas, translated as Down There or The Damned, is a novel by the French writer Joris-Karl Huysmans, first published in 1891. It is Huysmans's most famous work after À rebours. Là-Bas deals with the subject of Satanism in contemporary France, and the novel stirred a certain amount of controversy on its first appearance. It is the first of Huysmans's books to feature the character Durtal, a thinly disguised portrait of the author himself, who would go on to be the protagonist of all of Huysmans's subsequent novels: En route, La cathédrale and L'oblat.
Title page of the first edition of Là-bas.