The Forggotted Underland of now, only exists because of the plastic trees that man created...  

 

There was a sudden burst of light and then this obstacle course structure was placed. Plastic trees appeared out of nowhere in the mud one day. The Forggotted Underland Beings had no idea what this was but they made it function so it became part of their home. 

 

As the years went on only more of the same came, more tubes, more tunnels to explore. The Forggotted Underland Beings started to create more interesting  landscapes as the plastic trees were added to a landscape of mounds and hills.