It’s very hard for me to remember this, but I’m sure it was about a boy and a slightly older girl. The world was a barren wasteland by the looks of it. I clearly remember a deserted desert (haha), and at one point they were walking in giant underground caves. The girl said “These caves were formed by *the giant worms/snakes*”. Can’t remember if they were walking through the skeleton of one or if they hear one coming but the boy gets freaked out.
I watched this movie 9-10 years ago, I honestly have no clue.