It was the realm of mist and ice (the name means “home to the mist”). Niflmheim was not home to any living being, but it did contain eleven poisonous rivers, all coming from a single source: a giant maelstrom called Hvergelmir.
Close to the maelstrom, the rivers would flow strongly. Yet, the biting cold was so extreme that even the rivers themselves would turn to ice further down the stream. The huge blocks of ice that were transported by the stream would result in an ever-growing expansion of Niflheim.
The ice of Niflheim would melt due to the heat of Muspelheim, which would result in water and the awakening of Ymir and Audhumla.