Grab a shovel, because we're digging in to see some animals with real underground cities. But who has the most complex subterranean home? Find out in this top 10 countdown. From a bird that creates a hole for its home by flying head first into a cliff to an insect whose excavating can be heard a mile off, discover that there's more to digging than a hole in the ground when digging is taken to the Most Extreme.
