It was not more than four feet high, and twice as wide, but it was many times as deep and was carpeted with a soft white floor of sand.

In some past age a little stream had trickled out of this cavern, and the far end of it made a comfortable bedroom for a sleeping bear when the temperature was fifty degrees below zero.
Ten years before Thor's mother had gone in there to sleep through the winter, and when she waddled out to get her first glimpse of spring three little cubs waddled with her.

Thor was one of them.

He was still half blind, for it is five weeks after a grizzly cub is born before he can see; and there was not much hair on his body, for a grizzly cub is born as naked as a human baby.

His eyes open and his hair begins to grow at just about the same time.