We can walk down the street and go to the grocery store at a moments notice because the food has already been prepared for us. A bear can not go to the store, it has to hunt its own food. Because of these reasons many animals spend the warm months eating and gathering and storing food for the long winter. Then during the winter these animals spend the time resting in dens or burrows, basically sleeping through the entire season. There are two basic places that animals hibernate in.
Bears choose to sleep in caves and dens.
Groundhogs tend to hibernate in burrows. To learn about bears click here. To learn about groundhogs click here.