A primal memory perhaps, of a warm cave and safety from predatory animals?

Then, as the fire was allowed to fall into embers, they took their rest in the warm, dim cave.

When nights darkness fell, they all swarmed back into the warm cave.

And they had a warm cave and we wished to join them but could not.

He raised the blankets, making a warm little cave, just tight enough for the two of them.

No food, no warm cave to sleep in, no family.

You think of a warm, inky cave and you got its mouth all right.

There was evidence that they hibernated during the winters in the warm caves.

He lived in a big, warm cave with his mother and father dinosaur.

There was just enough rope to make the sling and pad it with material from clothes they didn't need in the warm cave.