Uller Uprising

The big armor-tender vibrated, gently and not unpleasantly, as the contragravity field alternated on and off. Sometimes it rocked slightly, like a boat on the water, and, in the big screen which served in lieu of a window at the front of the control-cabin, the dingy-yellow landscape would seem to tilt a little. The air was faintly yellow, the sky was yellow with a greenish cast, and the clouds were green-gray. No human had ever set foot on the surface, or breathed the air, of Niflheim. To have done so would have been instant death; the air was a mixture of free fluorine and fluoride gasses, the soil was metallic fluorides, damp with acid rains, and the river was pure hydrofluoric acid.