My first impression was of vast space, a colossal reach of space that stretched far away before us, and into which our ship was racing on. And then I saw, with sudden awe and wonder, that this vast space was not the unlimited, unbounded space we were accustomed to, but was limited, was bounded, bounded by a colossal sheet of flowing flame that hemmed it in in all directions. Above and below and before and behind us stretched this mighty wall of flame, a gigantic shell of fire that enclosed within itself the vast space in which our cruiser raced, a space large enough to hold within it a dozen solar systems like my own. Stunned, we gazed out into that mighty flame-bounded space, and then I flung out a hand toward it in sudden comprehension. "We're inside the nebula!" I cried. "It's hollow! This vast open space lies at its heart, and those currents carried us down into it!" For I saw now that this was the explanation. Unsuspected by any in the Galaxy the mighty nebula was hollow, its gigantic globe of flaming gas holding at its heart this mighty empty space, a space mighty in extent to our eyes, but small compared to the thickness of the great shell of fire that enclosed it. And down through that fire, that vast ocean of flame, the currents of the nebula had brought us, from its outer surface, down into this great space at its heart of which none had ever dreamed, and into which we had been the first in all the Galaxy to penetrate. While we gazed across it, stunned, our cruiser was racing on into this vast hollow, away from the wall of flame behind us from which we had just emerged. And now, as we flashed on, Sar Than cried out too, and pointed ahead. There, standing out black against the encircling walls of fire in the distance, was a small round spot, a spot that was growing to a black globe as we hurtled on toward it, a globe that hung motionless at the center of this mighty space, here at the nebula's heart. We were racing straight into the great cavity toward it, and now there came a low exclamation from Jor Dahat, beside me, as his eyes took in the great globe ahead. "A planet!" he whispered. "A planet here--within the nebula!"