"Does it really matter, Charlie?" Jan asked, her eyes beginning to shine, now, some of the strain already disappearing. "Here's an old, old civilization, hidden, grown esthetic, maybe even a little decadent, but extending far. You know it, feel it! Here are beings changed to an android life-basis so long ago that it seems natural--hardy flesh healing if injured, children being born as in the old flesh! Even death almost a myth! Gosh, I hope we can get used to all that, Charlie! Peoples multiplying, spreading to the stars." "Don't paint it too bright, Jan," I laughed. "Come on. Let's explore farther." I don't remember how many hours we spent on that long excursion, or all that we did. There was more than one bubble cavern; there must have been thousands connected by artificially drilled passages in double arrangement for traffic moving in two directions. In those passages, currents of air carried one along swiftly. It was a perfect transit method for a micro-world. In some caverns were other cities. But there were more where tiny agricultural machines, with limbs like a beetle, crawled across miniature fields. Here we ate strange, sweet fruit, that surely contained the carbohydrates of familiar food. But no doubt it also contained radioactive salts from the soil in which it grew. As we had been, it would have poisoned us. As we were, it was a double source of vital energy, chemical and subatomic. Other caverns were murked with the fumes of electric foundries, self-operating, close to the mine-tunnels that bored deep into the natural, nickel-steel core of the asteroid. In still other caverns there were low buildings full of lathes, drills, presses, among those that we could name--all automatic, too. Then there were caverns where stood lines of square containers, enormous to our eyes, and joined by a network of cables. This must be a power source--banks of nuclear batteries. And in several adjacent bubble cavities we saw where an enormous metal cylinder was being built, each oblong segment being welded into place by mechanisms of the true robot variety. From any one cavern only a small part of the curving side of the tube could be seen. "Some kind of jet engine?" I asked almost rhetorically. "For their further expansion toward the stars? Like moving a whole planet to them, eh?" "Your guess, there, can be mine, Charlie," Jan said. We felt no physical tiredness in spite of all our activity. "Let's get back to a more idyllic surface bubble, Jan," I suggested, "and go swimming in water if natural law, here, allows it." "Crazy!" she responded gleefully. Air, rising in a vertical shaft, bore us aloft for the few feet that, to us, stretched into seeming miles. Against what appeared to be a green hillside, we soon found what we sought, a great, clear ovoid, glinting like a lens in diffused sunshine.