The Atomic Bomb is originally described, in Chapter 2 of The Empty City, as follows:
Dave lifted the atomic bomb out of its dusty spot in the corner and placed it in the center of the table. It was a gray steel box about a foot tall, a foot wide, and a foot and a half long. The various seams were closed with an excessive number of bolts; where one bolt would have been sufficient, four had been used. The designer clearly did not want the box opened. The words "ATOMIC BOMB" were stenciled in black along the top of the front panel. Below that, on the left, was a large red button labeled "DETONATION SWITCH: DO NOT PRESS." On the right were a number of small lights and a big red digital counter, above which were the words "SECONDS UNTIL DETONATION." Dave brushed a thin layer of dust off of the top, revealing a hand-painted radiation symbol and the words "HANDLE WITH CARE."
Not long after we first moved into Wunderland, Kat Dutton's mom took this photo of her, and they used it as their Xmas card that year, with the caption "Peace on Earth":
This spawned a whole tradition for us: Taking photos of people pushing the button on our Atomic Bomb. We filled a whole wall with bomb photos, starting with the one of Kat seen above. Then we took it down, and started again, and again it fiilled up. So we took it down another time and started over, and that time, we also started putting them on the web.