Origin: The Hellbound Heart by Clive Barker
They offer experiences which are far beyond that which this world can provide. Cenobites can bring about "...conditions of the nerve endings the like of which [one's] imagination, however fevered, could not hope to evoke." They were once human, and in their desire to experience more than the reality they knew they chose to open the box, eager for the journey to hell. Scars cover every inch of their flesh which is "...cosmetically punctured and sliced and infibulated, then dusted down with ash." They smell of vanilla and are invisible and inaudible to people who have not solved the Box.
They must be summoned by a device such as Lemarchand's Box to cross the Schism into this world. They cannot reseal the Schism until they take someone back with them (only blood and flesh can bring humans across it). Other ways to summon the Cenobites can be found "...in the vaults of the Vatican, hidden in code in a theological work unread since the Reformation." or "...in the form of an origami exercise, [that] was reported to have been in the possession of the Marquis de Sade, who used it, while imprisoned in the Bastille, to barter with a guard for paper on which to write The 120 Days of Sodom."