Tertullian

By ourselves the lower regions (of Hades) are not supposed to be a bare cavity, nor some subterranean sewer of the world, but a vast deep space in the interior of the earth, and a concealed recess in its very bowels; inasmuch as we read that Christ in His death spent three days in the heart of the earth, that is, in the secret inner recess which is hidden in the earth, and enclosed by the earth, and superimposed on the abysmal depths which lie still lower down. Now although Christ is God, yet, being also man, "He died according to the Scriptures," and "according to the same Scriptures was buried.