Not sure if this was what you had in mind but here is my response to the potions challenge.
Harry potter does not belong to me; neither does the hollow earth theory OR Tunnels. Cascade-The-Narrorator however does.
Meow-Bill Weasley
Meow- Gabrielle delacour
Meow- Harry Potter
Meow- James Sirius Potter
Meow- Peter Pettigrew
Meow- Blaise Zabbini
Bill Weasley strode in to the ancient temple. . .
Gabrielle delacour followed him sliping past traps silently
The rat, Peter Pettigrew followed unnoticed
In retrospect they should have noticed-the temple was sealed
Didn't notice Pettigrew setting up vials of a smoking potion
Seven year old James Sirus Potter was digging around in the attic.
As he pulled out an old jacket, something teetered and fell. It was an old wooden box inlaided with gems. Picking it up he walked out of the room in search of his father.
Harry potter was surprised to see his son walk in in the middle of his conversation with Blaise Zabbini. Then he noticed something infidently worse than James possibly eavesdropping. He was holding the Epic time turner box!
Hmmm whats In this said James taking the lid off the box.
James NO! Harry shouted running over to him, Blaise right behind him.
What has Harry's foolish son done this time, though Blaise.
But it was too late, for when James touched it they touched him and were transported back in time.
WHAM!
They landed in a tangle of limbs and torsos in the inner sanctum of the temple just as Bill, Gabrielle and Pettigrew walked in.
Sizzle Fizz POP
BOOOOOOOOOOOOOOMMMMMMMM!
BOOOM BOOM BANG BANG
CRIEEEK
BOOM!
FOOSH
James knew he was dead- not dying dead. Why else would he not know which way was up or down.
Falling, as Gabrielle regained consciousness this was the 1st sensation that greeted her. Opening her eyes, what she saw shocked her. They were in freefall, down a black pit. She watched this for several minutes. Everyone else was a little above or below her.
Bill recognized the sensation of freefall. After all this wasn't the 1st time he'd fallen down a deeeeeeep pit.
Everyone else remained unconscious until they splatted on to fungus.
Harry awoke in a strange substange, it felt like he was laying down in squishy, wet foam. It smelled awful. And felt awful too. Harry extracted himself from the whatever-it-is with a loud SQUORP. Then he looked down EWWWWWWWWWWWWWWWWWWW, EW, EW, ICKY, GROSS,GET IT OFF!
Harry's sreams awoke the others who then attempted to remove themselves with varying degrees of success, stated a grey eyed bond AKA Cascade the Narrorator
Who the F- are you creepy stalker girl?
I'm not a stalker I'm the Narrator, Cascade.
Where are we?
You jumped-or fell down one of the seven sisters, which is called Thundering Willow.
Why?
Subterranean air currents- not really unusual phenomena.
Were underground! How far-
YIPPEEE I'M ALIVE!
- down are we?
About 21,000-
ALIVE! ALIVE! ALIVE!
-Feet down.
Should't we be dead?
Obliviously we aren't.
World is hollow a$$tards; get used to it. So do you have a way of getting Topsoil or do I have to teach you how to survive down here?
BOOM bang CLATTER SPLOCH SPLOCH SPLOORCH
Wait you don't have something that explodes do you?
Yeah we do. . .
Right so here's what were gonna do. Use your exploding stuff and the reduced gravity to blast us all topsoil.
So we got the stuff; they called it ''exploding potion'' but I just call it our way out here.
We only have one shot at this guys- make it count.
Oh I'm not worried how 'bout you guys.
Three, Two, One we all chanted as the 1st series went off.
As the blast force ratted my skull we were propelled upwards past strangly geometric versions of fungal shelves.
As we were blasted upwards, i told them we were from the future.
WHA. . . ?