Other forms: hibernacula
If a cave is handy, a bear might choose it as its hibernaculum, a place to spend the winter while it's in a state of winter dormancy. A groundhog's hibernaculum is an elaborate underground burrow in which it spends the winter in a deep sleep.
The word hibernaculum is borrowed from Latin, where it means "winter home." It's related to the English word hibernate, which is what some animals do to survive the harsh, winter months: They go into a deep, prolonged state of inactivity. A hibernaculum can be as simple as a hard, protective covering on an insect (or plant), or a pile of leaves to snuggle down in. While hibernaculum is a specific term in zoology and biology, it may be used figuratively to describe a person's winter retreat.