Burrowing Bunyips

In Turien, Bunyip is a monster-like entity akin to aether - they don't exist, presumably, but they are used for anything that could have been or could be. For example, the origins of the original caverns of the Underground. 
A group of Humans branched off to explore the Underground around 4500 years after the creation of Turien. There was a large entrance carved out from a hill and it slowly travelled underground, spreading into a number of large caverns that extended far below the surface of Turien. How these were formed, and why they hadn't been noticed over the centuries was a mystery.
And where mysteries are involved stories arise...

Praying on the dreams and nightmares of children were the monsters known as Bunyips. But as children grew up, they became adults. And these adults remembered. Not wanting to let their children wither in any way, they waited until their children went to sleep and watched in the silent dark until the Bunyips came. Lighting up fires and magic, they killed a large portion of the Bunyip population.
After being chased out of the Swamplands by the Frog-kin and Snake-kin, the Bunyips scaled Turien for a home. Being kicked from the forests, the plains, and the desert the Bunyips went to the badlands. But then war approached the badlands and the Bunyips had to flee again. The only place was left was Underground. Yet they could not dig. 
The Bunyips did have some small magic, in that they could hide themselves in swampland, as well as grow swampland. One Bunyip took it upon himself to create the majority of a new, hidden, swampland within the hills between the plains and the desert, letting his companions hide within the swamp and rest.
An ailing Fairy, hurt from the war, came to the swamp. Blinded and dehydrated, she asked for water. The Bunyip obliged, cleaning a section of the water to be fit for drinking, hoping to keep his companions hidden. The Fairy drank and slept. 
Hunger brought forth his companions out of the water. Seeing the Fairy, they lunged to eat her dreams, but the Bunyip who gave her water stood in front of them. He was slashed by his companions, but did not let them eat her. The Bunyips went back to hiding in the swamp, leaving their companion alone to die. She wasn't a child anyways, her dreams would be bitter.
Before he did an Elf found its way to the swamp puddle. Seeing the clear water and the dying Bunyip he raced to the Fairy, his master. She awoke and he told her what he saw. She was not surprised of the swamp and its inhabitants, but the sacrifice of the Bunyip who gave her water. She asked her disciple if there was anyhting he could do. The Elf thought for a while, then nodded. 
Utilising his land magic, he opened up the ground and drew a large and complex cavern system. Then he took his master away, without telling the hiding Bunyips any specifics, hoping they would get lost in return for looking at his master as a meal. 

One version portray the Bunyips as eating the children and being on the run from mother's grudges afterwards. Another version portrays the Bunyip as Beast-kin who were deformed at birth, and treated as the monsters that ate the children, instead of the children themselves. Some versions leave out the Fairy and Elf entirely, having the Bunyips create the caverns of the Underground themselves. And some versions have the Bunyips ensalved to the Fairy, forever digging tunnels and caverns as eternal punishment for what they did to the children in the beginning.

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