He was conscious first of a mighty curving roof of rock close above him, from which the disk was dropping smoothly downward, and in which there yawned a black circle which was the opening of the shaft down which he had come. A full mile below lay the floor of the mighty cavern, stretching away for miles on every side, a colossal underworld lit by the crimson, wavering glare. Then Rowan's stunned eyes made out, far away, the titanic, precipitous walls of gray rock which formed the great cavern's sides, miles in the distance, stretching from floor to rocky roof. And as his eyes swept along them they came to rest upon the blinding, dazzling source of the crimson light that illuminated all this cavern world. In the gray wall to his right, miles away, was a great, slitlike opening near the roof, an opening through which there poured down a mighty torrent of blazing, liquid fire, a colossal Niagara of molten flame whose crimson, blazing radiance shot out a quivering glare which lit luridly the whole mighty cavern. For thousands of feet the great torrent of raging fires tumbled downward, caught at the base of the cliff in a canal of gray stone which conveyed it, a river of living flame, into a central basin of stone of the same diameter as the great shaft above, and which lay just beneath the opening of that shaft in the roof and beneath the descending disk, a lake of leaping flame. Around it were grouped a circle of strange, blunt-nosed machines of some sort, and down toward it the disk-platform was smoothly sinking. And beyond and around it, on the stupendous cavern's floor, there stretched mass upon mass of huge buildings, gray and mighty and ancient in appearance, buildings which resembled masses of gigantic gray cubes piled upon each other in neatly geometrical designs. Broad streets cut through their square-cut masses, and in those streets moved great throngs of large and smaller shapes, mighty dinosaurs and masses of the lizard-men. Far away to the distant, encircling walls stretched the massed buildings, and over them hovered here and there great pterodactyls bearing lizard-riders, flitting across the cavern from place to place on their immense, flapping wings. Rowan stared, stupefied, stunned, crouching at the edge of his descending disk, and then became suddenly aware of fierce and increasing heat beating up toward him. He looked down, saw that the disk was dropping straight toward the lake of fire below, sprang to its edge in sudden fear as it dropped on.