There was no waiting ambulance in the driveway. I descended the stairway, twelve metal steps railed in on both sides, feeling grateful for what she'd said right after I kissed her. "Don't worry about your wife. If Wendel tries to make us send for her we'll find a way to roast him over a slow fire until you're together again. There are three doctors who will put up a stiff fight and I'm going to set to work on all of them. You've no idea what a hospital can do with just the right kind of delaying tactics." It took me less than two minutes to half-encircle the driveway, take the turn she'd recommended and strike out for the Colony between the towering gray walls of the aerators. The Big Grayness. I'd seen photographs of that tremendous engineering project in my hell-bent-for-adventure years, when I'd sat at a desk in a schoolroom, and imagined what it would be like to take part in the construction work, standing on a dizzy height with an electronic riveter in my hand, watching blue lights go on and off and sparks fly up into the cool Martian night beneath a wilderness of stars. The reality was very much as I'd imagined it as a school kid, except that I wasn't a construction worker looking down over it, a human fly with a man-size job to do, but a guy that kid wouldn't have recognized, his footsteps echoing on the catwalk at the base of it. I had a giant-size job to do, but how could he have known it would some day turn into anything _that_ big? It wasn't even a project anymore--half of it still in the blueprint stage. It was completed and the towering gray walls were firm and solid, and the grills were sending oxygen spiraling out over the Colony without making me feel light-headed at all. Right at that moment I'd have welcomed a little oxygen intoxication but the aerator-system didn't work that way. The flow was regulated directly at the source, kept under controlled pressure and diffused outward high up by rotary circulators. As it spread out over the Colony it was drawn down to breathing level by another system of circulators, stationed at intervals about the Colony and extending twenty-five miles out into the surrounding desert. If you wanted to experience oxygen intoxication you had to strap a tank to your back and breathe the stuff in through a tube in the old way. But no one in his right mind would do that deliberately, for an excess of oxygen can be five-ways dangerous on a planet where what you have to worry about most is over-stimulation. There were catwalks on both sides of the aerator walls, with a central lane wide enough for vehicles to pass in opposite directions. I kept to the right hand side all the way to the Colony, and it took me about thirty minutes to get there. My strength amazed me. It probably wasn't quite up to par. But I only had to stop twice to rest and then only for a minute or two.