Complex sentence: From his mysterious book Warren apparently deduces that doors or stairways exist between the surface world and the underworld, through which demons may travel and he encourages Carter to travel with him to the location of one such portal, an ancient graveyard near Big Cypress Swamp.
Split into simpler sentences: From his mysterious book Warren apparently deduces that doors or stairways exist between the surface world and the underworld through which demons may travel. He encourages Carter to travel with him to the location of one such portal, an ancient graveyard near Big Cypress Swamp.